Doctors working on Shabbat

Question: What are some general guidelines regarding the halakhic permissibility for Jewish doctors to work on Shabbat?  I know that saving lives generally overrides Shabbat, but I am curious about less black-and-white situations that may occur on Shabbat, such as having a shift where one must be in the hospital or be on call, receiving medical training, etc.  Also, in a practical halakhic sense, are there any situations in which the appropriateness of violating Shabbat would depend on whether the patients are Jewish?  I'm sure that these are not simple questions and that there are likely multiple opinions on various issues, but some insight into this topic would be welcome.
Comment: http://judaism.stackexchange.com/questions/9146/why-is-it-necessary-to-ask-a-rabbi
Comment: [This article](http://www.yutorah.org/lectures/lecture.cfm/735806/Dr-_Fred_Rosner/Rabbi_Moshe_Feinstein-s_Influence_on_Medical_Halacha#) By Dr. Fred Rosner (author of several works on medical ethics) has a lot of the info you seek - the short answer is that most things are allowed if necessary, and a shinui is often employed.
Answer: I'm sure there are several lectures on YUTorah.org about this; probably an article or two in Journal of Halacha & Contemporary Society as well.  But in short:
"having a shift where one must be in the hospital or be on call" -- we generally try to avoid putting ourselves into a situation in which a matter of life-or-death might occur which would necessitating violating Shabbat; this "try to avoid" can be balanced out by other considerations, though.  (That's one explanation given for why the Mishna prohibits getting on a ship too close to Shabbat -- a life-or-death situation may occur -- but if taking the trip is a mitzva, it's allowed.)
"receiving medical training" -- a tough issue, as usually the life-or-death situation must be fairly immediate, not "oh this may allow me to save some life out there someplace, ten years from now."  Nonetheless, I'm told that Rabbi Dovid Cohen of Brooklyn has allowed people to take residencies that may require working on Shabbat.  But check with your own rabbi.
"are there any situations in which the appropriateness of violating Shabbat would depend on whether the patients are Jewish?".  That's easy.  No.  The Halacha is that we violate Shabbat to save any human life; that's the Halacha, that's the practice, that's what we do.
Comment: Do you have a source to your last statment?
Answer: First of all, being a doctor and healing the sick is not considered a Malacha (work on Shabbos). It is considered a Chachma, a gift, not a trade. See Rambam Hichos Refuah.
There is a fantastic Steera (contradiction) found in the Rambam which points this out. In Hilchos Shabbos, the Rambam holds that one is prohibited from carrying an amulet, since (medically speaking) they are of no use. However, in Hilchos Refuah, Rambam states that one can use (carry) an amulet since the ill person believes in this amulet (an amulet must be considered Mumcha, one which has been proven by healing the sick already), and healing is 60% in the mind, therefore the ill will be healed. As you can hear, the Rambam didn't sound like he was in favor of using tricks or the like. But if it works, any port in the storm!
Next question, is one allowed to transgress the Shabbos to heal a Goy? Technically no. However the Chachamim stressed that if they knew this they would kill us, therefore it is in our best interest to heal them ("משום איבה"). I fear to add this but Halacha is just that.
So, can one heal an animal on Shabbos? Basically no. However, one can make the animal comfortable until a doctor can administer to the animal. There is a wonderful book Sefer Tsar Balay Chaim by R' Itchak Nachman Eshkoli written in the last 10 years which deals with anything & everything to do with animal suffering. My son-in-law used this while writing a paper on Feeding Animals on Shabbos while in YU. I highly recommend this sefer to anyone who has an animal, especially since Tzar Balay Chaim is a Torah Issur and it is important to know what one can or shouldn't do.
Medical Halacha is well researched by the likes of Dr. Fred Rosner, Rabbi Dr. Abraham S Abraham (Nishmas Avraham), and many more. There are many Rabbis who write on medical halacha. Although that is a subject for another time indeed!
Comment: Rambam Hilchos Shabbas 2:12 אין מילדין את העובדת כוכבים ומזלות בשבת ואפי' בשכר ואין חוששין לאיבה ואע"פ שאין שם חילול. אבל מילדין את בת גר תושב מפני שאנו מצווין להחיותו ואין מחללין עליה את השבת

Doctors working on Shabbat


Can I link between notes in Evernote?

Question: For example, if I wanted to create a note about gifts to purchase for others, and then had a note for one of the people on those list, could I link the notes between each other?
Answer: This feature was introduced by Evernote for Windows and Mac users in June 2011. More information in this Evernote blog post.
Comment: The link no longer exists, that's why it's a bad idea to only link to something.  Should've copied the instruction part as well.
Answer: There's no way to link to notes that will consistently work on all the clients. It's one of the most requested features, and it is "definitely planned" by the developers. [source]
There's a hack to doing it on the Mac by using the exploit of spotlight, however this will only work on the same Mac. As well as linking to notes using the web client, however this will force the notes to be opened up in a browser.
Comment: This answer is outdated. See answer below about new feature added to Evernote in June 2011: http://webapps.stackexchange.com/a/19754/17203
Answer: This feature is available in Evernote for Mac 2.2 Beta 1, and Evernote for Windos 4.4 Prerelease (and, assumably, in future standard releases).
"Copy Note Link" appears under the Edit menu.  It is also available in the right-click menu on notes. This link can be pasted into Evernote or another application.
If pasted in a plain text document, you can see the link is of the format:
evernote:///view/...
Answer: insert an URL to the note you want to link to.
Comment: That may work OK if you use Evernote via Web, but will have problems when using Evernote client in offline mode (which is for me main reason for using Evernote).
Answer: There is a way to link notes, but it's a bit of a workaround.  Create some kind of random generated string and insert the same string into all the notes you want to link together.  Then use Evernote's search function to identify all the notes linked by a specific string.

Can I link between notes in Evernote?


Is packet radio possible on Baofeng UV-5R and similar HTs?

Question: I am curious to know if it is possible to do packet radio on VHF/UHF using the UV-5R... I have seen some invasive hardware hacks, but without modifying the radio itself (firmware, hardware) it's my understanding that you can only toggle send/receive using the 2.5mm/3.5mm TRS ports.
Comment: Apart from those mentioned below by rclocher3, there are many digi-mode that interface with transceiver with mic, speaker and PTT tx lines.  Use PC build in sound. No extra cost. Just get software, most free. Happy trying them out.
Answer: You sure can. It's been done before with a Baofeng HT, a Raspberry Pi, a USB sound card, and some custom cables and some open-source sound card modem software. This article explains a step-by-step approach.
This article shows how to create a custom cable for interfacing a Baofeng HT with an Android phone (but should be sufficient for figuring out the wiring for the USB sound card so you can interface with your Raspberry Pi - specifically, you'll probably need to separate the right/left audio from the mic and PTT for the sound card's separate mic/audio jacks). Of course you could use the custom cable and an Android phone or tablet running the APRSdroid software mentioned in that article. There are also ready-made cables like the BTECH APRS-K2 TRRS / APRS Cable.
In the first case, the Raspberry Pi is acting as the TNC; in the latter, the Android and APRSdroid are serving that function.
The point of this cable is to connect the input and output audio cables of your computing device (smart phone, raspberry pi or whatever) to the radio. By setting the VOX and squelch settings just right (e.g. "VOX at ~2, Squelch at ~1"). Then the computer takes the role of the modem and does modulation (for transmitting, triggered by the VOX setting) and demodulation (for receiving, triggered by the squelch setting).
I hope this helps.
Comment: Looks good. I'll take apart my extra headset and start gathering the bits I need to build it. Thanks.
Answer: The easiest way now is to get the Btech APRS-K2 Cable: it allows you to receive and send audio to the radio with a single cable. You can use it with the aprs.fi app or with a variety of software from a computer.
Comment: Yep, originally, I bought the usb data cable, but this APRS-K2 cable is what I was really wanting. With this, in theory, all you should need is software modem software to transmit digital data.
Comment: I've got a data cable which gives me a serial port. It can be used to program channels etc. The TRRS jack on this cable could be good for transmitting audio with VOX enabled. Upvoted.
Answer: In the end I used 'amodem' ( see https://github.com/romanz/amodem ). After a few calibration steps, I could get decent I/O rates - considering the nature of the medium.
Compression of archives is necessary, and may be considered unethical. But the compression algorithms (e.g. 7zip, xz) are public, and anyone paying attention can read the data.
Rates of >=19200 baud (~2.4kB/s) are easily accomplished internationally, while IIRC 57600 baud (~7.2kB/s) are realistic domestic.
Hope others can use this as an intro to PR.
Comment: So clearly-named zip-files is the way to go. Thanks. What kind of throughput did you get with PBBS, frequency/antenna info is welcomed as well.
Comment: I was based at the Alaska National Guard building on Fort Richardson and we had a half-wave vertical hanging off the same tower used by the state troopers.  Out transmitter was 100 Watts.  I am searching my memory for actual speeds, but I can tell you that it was sufficiently fast that I don't recall any discussion about it.  Back then, though, I am sure we used a TAPR-2 TNC.  That would mean 1200 bps.  9600 Pactor was just coming around but we needed to ensure maximum compatibility with anyone who could set up.   It operated on 145.010 and had very good coverage due to the location.
Comment: I used and ran PBBS for a long time, and the rules clearly state that licensees are not to even attempt to hide the nature of their communications.  That does not cover downloading ZIP files on a PBBS.  The intention is quite clear.  And anyone running a pirate-style fixed station in ham frequencies will be found and the FCC will do what they do best to them.  Compression of clearly-named, appropriate compressed files clearly is ethical.  It is a responsible way to conserve channel utilization and is to be encouraged.
Comment: btw, we used ZIP files only for programs.  Most of our traffic was plain text.   During disaster scenarios the system got busy in both directions.
Answer: Sure it's possible.  You'll need some sort of Terminal Node Controller (TNC), either one implemented in hardware or software, plus a set of cables that plug into the  2.5 mm / 3.5 mm TRS ports.  If you're using a hardware TNC then you'll need some sort of computer and a serial or USB cable between the computer and the TNC.  I've used a different model HT to send and receive APRS packets with a TinyTrak 4 as my TNC and xastir (APRS software for Linux), and it worked fine.  APRS is a protocol that sends and receives specially-formatted AX.25 packets.  I've heard there are "software TNCs", i.e. computer programs that generate audio tones to be sent to the radio, but I can't vouch for how well they work, having never tried them.
Comment: @user400344 TNCs, even used ones, seem to be quite pricey, because they were expensive when they first came out 30 years ago.  Given those prices I'd probably experiment with software TNCs.  If you want to do packet rather than just broadcast the location of your car via APRS, then I'd advise investing in a good antenna up high, and possibly a 50 W radio, before sinking money in a TNC.  You need good signal-to-noise ratios for packet, especially if the other station is another home station rather than a digipeater atop a mountain.
Comment: What cheap/old TNCs would you recommend I look for on eBay?
Comment: Well, the good news is that you're not the first person to want this.  I'm sure you will find a software solution.  As for hardware I think the best way to do this is with a USB sound interface and a cable like this:   https://smile.amazon.com/gp/product/B01LMIBAZW - these little sound interface units work with both PC and my Android tablet with the USB port:  http://www.ebay.com/itm/5-1-USB-Sound-Card-External-USB-Audio-Sound-Card-Adapter-Mic-Speaker-Interface-/291874480027 - I can't recommend specific products here; just showing these as examples.
Comment: @rclocher3 has a really good point (+1) - a good radio and antenna do need to come first.  Make sure you can hear other packet activity from your location.  You want to be able to make solid connections to others.  Scratchy sound doesn't work well with sound card interfaces or actual TNCs.  You want enough power that they can hear you also.  That means both transmitter  power and a good antenna installation.  As for TNCs, the prices have really surprised me.  Even the little MFJ-1270  units are now more expensive than they were in the 80s.  So starting with a sound card approach makes sense.
Answer: I recommend against using the modern inexpensive HT radios for packet, especially if you are buying the equipment on purpose for that application. You'd be much better off with 30-year-old used ham radio mobile gear, with more power, more selective receiver, more predictable operation, easier UI, and less RF into your digital equipment, easier connections, easier power hookup, and nearly the same cost.
A serious consideration with modern HTs is that the designers are interesting in optimizing voice quality and battery life with no consideration for how this impacts packet radio use.  Sacrifices can easily be made which increase usability for voice, but which make packet radio work worse and be more difficult to align.
Audio level consistency.  A packet radio receiver modem wants to see an audio level that is both consistent across a packet, but also nearly the same for multiple tone frequencies on a packet.  FM voice radios don't need to behave in this way.  Indeed, voice compression, bad for packet, actually sounds great on voice.
DC signals (BIAS) on the receive audio are also OK for FM voice, especially with built-in speaker equipment, but this also is of questionable value for a packet radio modem.
POP and CLICK removal: It is easy to remove pops and clicks from the audio by replacing annoying wave forms with duplicates of preceding or following wave forms, or by shifting the time of the wave forms.  This is a well documented (and no longer patented) scheme used originally in broadcast radio transmission.  This makes the receiver sound much better, at low cost, but makes packets less reliable, and this effect is nearly undetectable without an analog equipped logic analyzer.  It's very confusing.  I have on low authority that this is done in modern 2-way FM radio-on-a-chip devices.
Battery saving by disabling the radio: By having the control processor leave elements of the radio disabled for periods of time the radio can use less battery power while quiescent, but it would also not be awake to notice the start of a packet message.  Baofeng radios are replete with this technology.
The Chinese brand-name radios have been known to emit energy at frequencies outside the ham band at levels beyond those permitted by the various government radio authorities (D.O.C. in Canada, F.C.C. in the USA).  They have also been known to emit radio waves at near transmission levels through the chassis which can impact the stability of DC wiring in the vicinity of the radio.  This is also confusing to somebody new to integrating digital, audio and RF equipment.
Used 2-way or ham radio equipment is particularly applicable to packet radio.  A used ham radio which is missing the critical CTCSS PL TONE generator is nearly useless for repeater operation but is very usable for packet radio.  Kenwood TM2550, TM7950, TM7800, are perfectly fine packet radios and are 25 watts output or better.  Yaesu and Icom have offerings in the same age-class.  Because they are not useful to non-packet hams, they show up for low prices, even competitive with brand new Baofeng UV5R radios.
In the commercial 2-way market, the Kenwood TK705d or TK805d is a fine radio for packet.  Those are on ebay at under $50 delivered, even as I type.  While some commercial 2-way radios need PCs and software to program, the TK705d and TK805d are front panel programmable, or can be made that way by moving or adding a 2-pin jumper.
Answer: I built a homebrew interface that uses a small USB soundcard with mic and ear 1/8" jacks. Each of those drives a 600:600 ohm transformer.
On the radio side, the transformers drive the mic and ear connections via the 2.5 and 3.5mm jacks.
I also used a cheap USB to serial board to run an optoisolator to trigger the radio PTT. The reason for this is that if you use the radio VOX to initiate transmit, the radio will stay in transmit for some time after the data have been sent, and it misses the return data from the packet server. This took me some time to discover!
All that being said, I have found that it is hard to set levels properly, and my connection reliability has been spotty. I have been able to send/receive email using Winlink Express along with soundmodem software, but quite often, the system just keeps trying to connect without success, so I'm not sure that using the Baofeng radios is the best solution.
Answer: I was able to get a Baofeng HT working with packet, but had to adjust a number of menu items.  (The tricky one that is poorly understood is Squelch Tail Elminate or STE.)  My suggestion, assuming you're using something like a signalink to do PTT:

Set "battery save" mode to OFF (menu #3).
Set TDR-AB (menu #34) to A - this ensures your radio transmits on channel A.
Set STE to OFF (menu #35)
Set RP-STE to OFF (menu 3#6)
Turn "roger beeps" off (menu #39)
Set VOX off (menu #4)

If you're not using something external to handle PTT, you may need to leave VOX enabled and set to ~2.
Answer: Save time and aggravation. Get a Mobilinkd TNC-3 with cables and a ferrite bead for less than $200. The AFSK cables don't work well with VOX since (at least my cheap UV-5R) adds a hang of a few seconds after the tx ends. Not so with the Mobilinkd. UV-5R works pretty flawlessly with the TNC-3 and APRSdroid as well as MixW on my laptop. It is well worth the dough.
Comment: Welcome to ham.stackexchange.com!
Answer: As others have mentioned, it will work, but it won't perform as well as other options.  I second the suggestion of using a used commercial radio instead.
The biggest reason for my suggestion is that radios based on the RDA chipset have a rather slow turn-around time.  If the station you are connecting to is configured with a long enough TXD (TX Delay) you won't have an issue.  IF that station is tuned for higher performance, you will miss the reply packet entirely, or not catch the entire thing which will result in a retry.  This causes QRM and is not good for anyone.


How to vote to close an off topic question?

Question: When I try to vote to close a question as being off topic, I can't because I must now choose a SE site that would be more appropriate. Unfortunately, the only option given is to migrate the question to Photo.stack exchange.com which is the site I think the question does NOT belong to. As far as I can tell, there is no way to select another SE site, even those I am a part of.
Answer: I'm not sure I understand what you're seeing - I see:
Close >

off-topic because...

And then there are the four options to pick as to why it's off topic.
To improve the options for migrations to other sites, we need to prove there is sufficient volume to justify the need, and these are better flagged for moderator attention in addition to being voted to close.
Answer: See also Can we have a migration path → superuser, graphicdesign, and video, please?. There have always been only a limited number of target sites, and apparently this is by design.
If a question really belongs on another site, vote to close with a custom off-topic note, and then flag for moderator attention -- moderators can migrate to anywhere.
Comment: I believe moderators can migrate to any site in the entire network, meta sites included. If you guys can't see the right site to migrate to, you can just flag it for moderator attention with the site you think is right, and we should be able to do it.


How can I get Italian meringue to thicken?

Question: I tried to make italian meringue and it was all going well until the meringue, (with the sugar syrup added), just didn't thicken and turned into 'royal icing'. Next time, how do I make it and what can I do to rectify now?
Comment: Sorry didn't notice your post until after I posted in a similar thread http://cooking.stackexchange.com/questions/69448/italian-meringue-deflated-after-adding-sugar/71179#71179
Answer: Try this: separate the white from the yolk 3 or 4 days before you want to make meringue. Keep the white in an hermetic box in the fridge and take them out of the fridge one hour before you begin. So the egg white foam will be more stable.
Another trick is to add some drops of lemon juice to the egg white right before you beat them.
Answer: I had this exact problem and I fixed it by beating the mixture on a slower speed. At first I was beating on high speed which I think was beating all the air out of it (ironically!). Try beating in a smaller container so the mixture is more condensed and on a low whisk speed for more time.


Is there any free good google or bing interactive map?

Question: I already have a list of the all stores with their lad and lon. I am looking to hook this list with map. map will display the store names and other key data. possible?
Answer: Both google maps and the bing maps API needs a licence if its on a password protected site. Google maps API is free if its on an internet facing and not password protected site iirc.
Check out OpenLayers if you need a 100% free alternative
Answer: It is possible to render Map in List View for XSLTListViewWebPart (XLV) using Google Maps.
Solution description
For storing geographical locations and visualizing it in Map is used Custom List. Custom List is based on Generic List with Custom Content Type and with View to render Map.
Map List View is implemented using custom XSLT style sheet and JavaScript rendering control for Map.
For implementation details please see my blog post Bringing Map functionality into SharePoint 2010: Rendering Map List View
Usage
After deployment of solution new List Template named GeoMap List will be available.
In order to visualize stores on map, we create list instance of GeoMap List.
After saving information about stores

switch to Map View to visualize stores on map


Advanced Search AND Operator doesn't operate for Multiple Tags Search (at least)

Question: Have discovered recently while searching for multiple tags. Even if Search operator radio button AND selected, search for two tags returns results with OR logic. Mean, there is a contact, which has several tags assigned; search by selecting, say, two tags contact has, returns contacts tagged by one of tags, not both of them. Double- and triple-checked. Sounds like a bug, but not entirely sure, since no similar complains found. Will anyone with similar setup (mean, contacts with multiple tags), confirm it works / doesn't work, please.
Comment: You can check this yourself easily by using one of the Demo sites
Comment: Oh, sorry, forgot about this option; have just checked at one of demo sites.and indeed, AND is not AND for multiple tags search.
Answer: I think the AND operator applies between fields, not within options of a field.
If you want to search TagX AND TagY you can do this in Search Builder.
Comment: The AND/OR was moved out of Basic Citeria in 4.7. The Search Criteria help note states: "When multiple options are selected within a search field the selections are combined using OR criteria (e.g. selecting both 'Group A' and 'Group B' will find contacts who are either in 'Group A' OR 'Group B' or in both).

By default the different search fields are combined using the AND Search Operator (e.g. selecting Tag is 'Age' AND Country is 'Canada' returns only those contacts who meet both criteria). You can override the Search Operator default for combining different fields in the Search Settings."
Comment: You're right, it's probably my misunderstanding of GUI elements placement: since AND/OR switch is located inside "Basic Criteria"  fieldset, it looks so logical it covers fields inside this fieldset. I think also, help note, attached to AND/OR switch states the same: https://nimbus.everhelper.me/client/notes/share/428744/bxv59aazuvs42upqr90s
Comment: Have tried to use an API for search by tag(s); have got an error (had to cut full sql query due to comment length restriction):  "no such field",
    "sql": "SELECT contact_a.id as contact_id ... FROM civicrm_contact contact_a  LEFT JOIN civicrm_entity_tag `civicrm_entity_tag-Belgium` ON ( `civicrm_entity_tag-Belgium`.entity_id = contact_a.id  AND `civicrm_entity_tag-Belgium`.entity_table = 'civicrm_contact') WHERE  ( contact_a.is_deleted = '0' AND `civicrm_entity_tag-Belgium`.tag_id IN (Belgium) )   [nativecode=1054 ** Unknown column 'Belgium' in 'where clause']",


Too little storage for sync blockchain

Question: already having some ETH on my mist wallet - contributed them a couple of month ago. I can't sync the blockchain as I have to little storage on my computer. Using OS X 10.11.3; ETH Wallet Version 0.8.8. I am only able to sync until 13 % of the blockchain.
Sending ETH (to my Jaxx Wallet) did work two days ago (without synchronization of the  blockchain) - now, however I can't send any. All transactions I am trying to send at the moment are not working, even though they are shown in my mist wallet transaction history (according to etherscan they were not processed). Any ideas how I could manage to get my current ETH form my mist wallet to some other wallet where I dont always have to sync the whole blockchain? Could it work with myEtherWallet by importing my already owned private key? Any other ideas? Thx :)
Answer: Yes. If you have your wallet exported from Mist, you should be able to send from MyEtherWallet 'Send Ether & Tokens' menu.
Answer: I am fairly confident that the issue here is nonces.
When you send a transaction a nonce is attached to the signature. This is a unique number which increments each time you send a transaction. It starts at 0.
The idea is that if you resubmit the same transaction it will fail. Only one transaction with nonce 0 can be sent.
With your first transaction it is easy. Mist sets the nonce as 0.
With the next transaction it gets the count of transactions (sent from your account) from the blockchain such that it can discern the correct nonce.
As you have not synced the full chain it sees no transactions from your account, sets the nonce as 0, and the transaction fails.
You either need to sync the whole chain or use a servicd that has synced the whole chain.

Too little storage for sync blockchain


Did the early Christian community on Iceland require the import of wine for liturgy?

Question: Roman Catholic liturgy requires wine, which cannot be produced in Iceland. Did the Christianisation of early Norse settlers entail a need to constantly import wine as a result?
Comment: Not writing an answer for this because I have no information regarding Iceland specifically, but obtaining proper sacramental wine was difficult even in Scandinavia proper. *Early Norse Christians thus resorted to using* ***beer*** *as a substitute.* The Pope officially forbade this in 1237, when a bishop heading for Greenland inadvertently killed everyone's buzz by asking Rome whether this was liturgically valid. Nonetheless the Norwegian church apparently received dispensation to use beer substitutes later, so it is probable that the locals ignored an unenforceable prescript.
Comment: @Semaphore And the bishop heading for Greenland was told to use just bread "as it is custom in other parts", so maybe they could go without the wine.
Comment: do recall that it was warmer back then and wine could be produced easily in latitudes as high as mid-England. Perhaps the degree of travel needed to transport wine is less than you'd think.
Comment: [This google books link](https://books.google.se/books?id=tuY11WRAYPoC&pg=PA307&lpg=PA307&dq=norway+early+christians+communion+beer&source=bl&ots=xYclw49TgR&sig=ACfU3U18-Z-wqjpWEh3v6qkqAXsIQDP0wQ&hl=en&sa=X&ved=2ahUKEwjX0crghN_kAhWFyqYKHXNmACQQ6AEwFXoECAYQAQ#v=onepage&q=norway%20early%20christians%20communion%20beer&f=false) might be a potential source for an answer. It looks like wine was imported, but (unsurprisingly) was no available in sufficient quantities. It also discusses the replacements the Icelandic Christians used, as well as the pope's ban on them
Comment: And what about the probable Irish monks before the Norse settlers?
Comment: @curiousdannii Sure, even on Ireland wine seems not to grow. Just wantet to keep the question short.
Comment: Counterquestion, does mead count as wine? :-D
Comment: A priest has the power to consecrate only bread with no wine, it would be valid and the bread would be the whole Christ (body, soul, divinity, etc), but this is illicit.  "Mass" means that both species must be consecrated, there is no half-mass. A bread-only desperate custom may even have existed in a remote place, but I would expect such custom to be prohibited as soon as Rome or an archbishop knows about it. Also remember that frequent communion is a quite modern custom, nobody there would complain about not being able to communicate every week. Priests often didnt celebrate mass every day.
Answer: Short answer
Wine was imported but was often scarce and always expensive. It was a liturgical requirement, but it was not one that was always (or even often) met without bending the rules a little.
When supplies ran out or low, substitutes were used, though by the first half of the 13th century the popes were clamping down on this practice. Given the distances involved and the reality of the situation with which priests in Iceland were faced, the popes' word was not strictly followed, though. There is direct evidence from the 14th century that wine was watered down, and mass was sometimes held without wine.

Details
Orri Vesteinsson, in The Christianization of Iceland: Priests, Power, and Social Change 1000-1300 notes that we have limited evidence but cites the case of a priest Reginpreht bringing wine to Iceland:

The Old German eleventh-century poem Merigarto mentions an excellent,
  learned, and honourable priest called Reginpreht whom the author had
  met in Utrecht and who had been to Iceland and profited greatly from
  selling grain, wine, and timber.

In the 11th century especially, there were frequent visits to Iceland by bishops, priests and monks from Norway. They may well have brought supplies with them. In the 13th century, there is evidence of wine being sent to Iceland as a gift:

...in a charter dated 1277, in Skallholt, it is stated..."that the
  bishop thanks him for the friendly words and the present which the
  king has sent him [of a] barrel of wine for the mass and a pound of
  wax and a pound of flour"

Source: Jesus Fernando Guerrero Rodriguez, 'Old Norse Drinking Culture' (2007 Doctoral thesis)
Also, in 1279, King Magnus VI of Norway

send[s] two barrels of wine to Bishop Arni Porlaksson

Source: Rodriguez
There is also evidence of wine imports (and the high price) from a 1420 charter in Vestmannaeyjar, Iceland:

It provides a price-list for trade between Icelandic and English
  merchants. According to it, one could acquire "iiij tunnur biors
  firir hundrat" (four barrels of bjarr for a hundred) while one would
  get "tunna vins firir klent .C." (a barrel of vin for a clean
  hundred). In other words, one could acquire 4 barrels of bjarr for the
  price of a milch cow or two marks and a half (i.e. 570 gr.) of silver,
  while a single barrel of wine would cost four times as much (roughly
  2.3 kg. of silver as pure as that used to pay for the four barrels of bjarr). That is, a barrel of wine was 16 times more expensive than a
  barrel of bjarr.

Source: Rodriguez
Other cases of imported wine are mentioned in the source provided in Nathan Cooper's comment:

...limited quatities of such beverages as wine, mead, and beer were
  imported, mostly from Germany. Earlier, wine had been purchased from
  England....

Source: Jón Jóhannesson, 'A History of the Old Icelandic Commonwealth: Islendinga Saga'
Nonetheless, wine was sometimes in short-supply

when trading-vessels failed to arrive. For this reason Icelanders
  began in 1203 to make berry-wine as a substitute for communion-wine.
  Bishop Jon of Greenland taught the Icelanders how to make this wine
  from crowberries....Berry-wine was then used for communion services to
  some extent until 1237, when the Pope forbade...

Source: Jón Jóhannesson
Wine was, unsurprisingly, very expensive. In Norway and Sweden, beer and heavily watered wine were used (and then banned by the pope). Many bishops and priests came to Iceland from Norway and brought these practices with them. Perhaps unwisely (as semaphore suggests in a comment), rather than keeping quiet about it,

In 1237 the archbishop of Nidaros, Sigurd Eindridesson (r. 1231–52),
  tried to convince Pope Gregory IX (r. 1227–41) that his most northern
  frontier needed special assistance because wheat and wine could not be
  produced locally. He even suggested replacing wine in the sacrament
  with beer or some other liquid. But the pope did not agree. The
  province of Nidaros, which consisted of Norway, Greenland, Iceland,
  and other North Atlantic islands, had to follow the same rules as all
  other Christian territories.

Source: Lars Bisgaard, 'Wine and Beer in Medieval Scandinavia'. In Kirsi Salonen, Kurt Villads Jensen, and Torstein Jørgensen (eds), 'Medieval Christianity in the North' (2013)
To what extent the Icelandic priests obeyed the pope is unclear, but they certainly watered the wine (see below). Not only was wine very expensive and Iceland even further away from its production centres than Norway, but also archaeological evidence indicates that Iceland was comparatively poor:

Orri 0steisson has noted...in the archaeological record) "[o]ne has to
  go pretty far down on the social scale of Norwegian (burials to find
  graves that compare with the richest Icelandic ones"

Source: Megan Arnott, 'Hveiti ok Hunang: Viking Age Icelandic Mead?'
Taking all the (limited) evidence into consideration, it is likely that, although wine for liturgical purposes was used when available, it was probably restricted both in the number of people who used it (mostly priests) and the frequency, and that substitutes (most likely beer) were sometimes used despite the pope's strong disapproval. Also, evidence of watering comes from a charter written in the 1320s:

in a charter written ca. 1323-28 it is stated that:..."([we] order
  also that all the priests, under the penalty of suspension from the
  office, that only them sing mass [and that] only the priest that sings
  mass blends water with wine in the chalice, and not the clerk, so that
  there is more water than wine in the chalice so that water is more
  abundant than wine."

Source: Rodriguez
Rodriguez also cites

A charter dated 1375, begins with the words "af pui ath vijn hefir
  ecki et cetera, (because we have no wine et cetera) instructs the
  priests to continue with the celebration of mass every Sunday.

(All emphasis is mine)
Comment: @Luiz Did you read this answer?
Comment: Water must be mixed with wine at every mass - Because the romans would almost always mix water on their wine, and the church strive to do the way it was done, to avoid the risk of invalidity. The usage today is to use a spoon to add a droplet. But I do not think that mixing a large amount of water would be an abuse - the romans often used 50%-50% or even more.
Comment: In the absence of wine/bread, there can be no consecration and thus there can be no  mass - but there would be still a celebration of the word, and even communion if there are still consecrated hosts available. It is probably what Rodriguez refers to - many people confuse mass with the non-mass liturgy, specially if besides readings there is also communion, people would write down "mass" anyway. But technically, no consecration under both species --> no mass: The central point of the Mass is the Eucharistic sacrifice.
Answer: The Church has always required that the matter for transubstantiation be wine made from grapes. This has be codified under:

Can.  924
§1. The most holy eucharistic sacrifice must be offered with bread and with wine in which a little water must be mixed.
§2. The bread must be only wheat [not barley, etc.] and recently made so that there is no danger of spoiling.
§3. The wine must be natural from the fruit of the vine and not spoiled.

Even must (barely fermented, unprocessed, unadulterated grape juice) can be used, if necessary.
If Icelanders don't have wine or wheat, they must obtain them somehow. This is generally what's done today. Much of the altar wine used in the U.S., for example, is imported from California (cf. Cribari). The same goes for altar bread. In the early missions in the southwest U.S., for example, vineyards were cultivated, some of which still exist today.
A sacrament with improper matter (e.g., baptism with motor oil, barley and apple juice in the Eucharist, etc.) is invalid.
Referenced in the Wittmann, P., & Remy, A.F.J. (1910). Iceland. In The Catholic Encyclopedia, the following work describes the Icelandic discovery of America ("Wineland"):

The Finding of Wineland the Good: The History of the Icelandic Discovery of America (1890) by Reeves, Arthur Middleton, 1856-1891
Comment: What did they do in Iceland 500 years ago? The question is about early Norse settlers.
Comment: @axsvl77 If they couldn't grow grapes or wheat, they had to import them.
Comment: @axsvl77 Did Catholic Masses exist in Iceland during those times?
Comment: https://icelandmag.is/article/ask-expert-what-largest-religion-iceland   I hope you can make your answer cover this entire time span! It will be very interesting.
Comment: *baptism with motor oil* - Early patristic writings speak of people living in certain desertic regions being baptized with *sand*.
Comment: @Lucian That's not a valid baptism. Why couldn't've they used saliva?
Comment: @Geremia: They would have, were deathly-sick sailors navigating on seas or oceans formed of such fluids to have been trapped there for weeks or months on end in that particular predicament. However, this is nowhere the case on Earth, hence the lack of need for such an indulgence.
Comment: The fact that the Church *requires* wine doesn't answer the question of what the Icelanders actually *did*.


Can the rogue repeatedly hide in combat to sneak attack the same enemy?

Question: One of my players is a rogue and has been, on his turn, using Cunning Action to hide as a bonus action and immediately afterwards attacking. I have been ruling that this does work to grant him advantage as an unseen attacker as I believe that is the RAW, but it seems a little strange. Is he really, in the span of 6 seconds, ducking behind a corner and popping back out and this completely disorientates his target? I guess I just wanted to make sure I was ruling correctly.
Comment: [many related questions](http://rpg.stackexchange.com/search?q=%5Bdnd-5e%5D+attack+from+hiding+is%3Aquestion)
Comment: related: [Can I use cunning action to get away and hide right away?](//rpg.stackexchange.com/q/90879)
Comment: related: [What advantages does hiding have?](//rpg.stackexchange.com/a/63453)
Answer: No, this doesn't work in melee.
At least not the important second half.

Yes, they can duck behind the corner and hide. All they need to do to be allowed to hide is break line of sight.
No, they can't just pop back out and sneak attack. To sneak attack, they need advantage, and to get that from being unseen they have to still be unseen when they attack (PHB, p. 195):

When a creature can't see you, you have advantage on attack rolls against it.

Unfortunately for the rogue, as soon as they pop out in front of an attacker that's already aware of their presence, they are immediately seen and no longer count as unseen when they attack (PHB, p. 177):

In combat, most creatures stay alert for signs of danger all around, so if you come out of hiding and approach a creature, it usually sees you.

Sneak attack only works if they sneak up on an enemy who doesn't know they're there. Popping out of hiding isn't sneaky, unless the enemy is surprised — and they can't surprise an enemy that is "aware of danger". When they duck behind a corner in combat, the enemy is aware of danger and watching all around, and is impossible to sneak up on (without unusual circumstances), because that enemy is the opposite of surprised — they are actively on guard.
Does it work at range?
Not easily. It can work as long as they avoid being spotted, but not being spotted is the hard part: since the attacker's location is automatically given away and after that it's easy to see them, special precautions are required to prevent being seen despite the target knowing exactly where they are.
To do that at range you're working with the same rules — they need to be unseen, they need to stay unseen until after they make the attack, and the target needs to fail to locate them after being attacked. It's that last part that makes this difficult — by an explicit rule, attacking reveals a character's location (PHB, p. 195):

If you are hidden—both unseen and unheard—when you make an attack, you give away your location when the attack hits or misses.

So to make this work at range, they need to arrange fictional circumstances somehow to defeat that. The usual way to do this with ranged attacks is to

attack while unseen (usually in cover1), revealing their location,
either have attacked while in cover, or move to break line of sight or into cover,
hide now that they're somewhere that allows a Stealth check,
move to a new location without that movement being seen, to make their location unknown again,
then, attack from their new location, unseen.

This convoluted process is often necessary because, at step (1) the ranged attacker has already revealed their location, and all it takes is a successful Perception check to see them (assuming the attacker is not blindingly obvious once the enemy knows where to look) for the advantage from being unseen to be removed. Steps (2)–(5) establish a new location that has not already been revealed, allowing the next attack to be made unseen.
(However, this process can be largely skipped if the hiding spot is so good that Perception checks to see the attacker are likely to fail. To be a good sniper, make a good sniper nest! And hope you're not seen, and have an escape route planned.)
But popping out from hiding in a single location before attacking?  No, that won't grant advantage, because just like in the melee situation, the attacker is immediately seen once they move out from their hiding spot to line up the next shot.
Ugh, this is too hard!
Well then, do it the simple way: an enemy that has an ally of the rogue's adjacent to it can also be Sneak Attacked. That allows Sneak Attack every round with no need to fiddle with movement or hiding or seen/unseen variables. Just flank and shiv.

1. This post uses "cover" in the dictionary word's tactical sense, to describe the activity happening in the game fiction. Whether that cover is mechanically represented with Obscurement (PHB, p. 183) or Cover (p. 196) will depend on the exact circumstances as adjudicated by the DM on the scene, as is appropriate.
Comment: You aren't revealed when you attack. You're revealed only *after* the "...attack hits or misses." If its after the attack hits, you get your SA damage.
Comment: Comments are not for extended discussion; this conversation has been [moved to chat](http://chat.stackexchange.com/rooms/65154/discussion-on-answer-by-sevensideddie-can-the-rogue-repeatedly-hide-in-combat-to).
Answer: Yes, but not without penalty
There is advice from Mike Mearls on this topic on Twitter. I recognise that the designers have not always been consistent, but on this issue they do seem to be.
The advice is this:

A creature can attack from behind cover, even just a tree, and hide again to repeat the process.
But when it attempts to hide again, it does so with disadvantage on its Stealth check.

So a rogue can repeatedly hide in combat to sneak attack the same enemy, but it's harder after doing it the first time, owing to disadvantage on subsequent attempts at hiding. Because it's harder for the rogue to hide, it's also harder to get advantage on the next attack for being unseen.
What else?
We can make some other deductions from the way the designers interpret the rules.
If you are hidden behind cover and you emerge to attack, are you still hidden at the point that you make the attack?
The designers unequivocally say that, if you are hidden, you can emerge from cover to make an attack with advantage. This means that, even though your target may have line of sight to you, you are unseen by it. And the only thing that can make you unseen in this circumstance is being hidden. So, if you are hidden, but come into a creature's line of sight, you can still remain unseen by it and hidden from it.
But that could get ridiculous couldn't it? Couldn't I just prance around right before your eyes, so long as I started hidden?
Agreed. I doubt the prancing was part of the designers' intention.
I think it is reasonable to assume that they did intend for you to be able remain in your current position, while peeking round cover to watch or aim an attack at another creature. There is also the errata that says that you can remain hidden if you are not clearly seen. Whether you're 'clearly seen' is a matter for the DM's discretion, but probably includes three quarters cover, which is what you would have if you were to peek out of full cover. It might extend to any partial cover or obscurement. But it does not extend to being in plain sight of another creature - so no prancing!
If your opponent has seen you move behind cover, can you hide from her?
Yes you can, but if she has a shrewd idea of where you are (eg you're very likely to be behind the tree she last saw you standing beside), you take disadvantage on your Stealth check to hide.
[As an aside, I think the designers are making a mistake here: your attempt at hiding isn't intrinsically worse, it's your opponent's ability to spot you that is better. So their Perception check should get advantage rather than your Stealth check suffering disadvantage.]
The take home message
If you are hidden, you can peer round cover without being seen and line up your shot; you have advantage on your attack. If you're not hidden, you are spotted as you peer round the cover so are no longer unseen; you do not gain advantage on your attack.
Once you have attacked in this way, you can attempt to hide in the same place again, but your check has disadvantage.
Comment: "If you're not hidden, you are spotted as you peer round the cover so are no longer unseen; you do not gain advantage on your attack." - I think this is a really important statement to understand. The purpose of Hiding is to be treated as if you are "unseen and unheard" in circumstances where you ARE visible. Explicitly described by Jeremy Crawford: "if the rogue has to come from behind corner/tree/cover to get a line of sight, that's ok? [Yes]" Good answer covering a lot of ground, lacking some quotes for mentioned sections though.
Comment: "There is also the errata that says that you can remain hidden if you are not clearly seen" are you referring to "The DM decides when circumstances are appropriate *for hiding*. Also, the question isn't whether a creature can see you *when you're hiding*. The question is whether it can see you clearly."? This errata applies to hiding, not remaining hidden. Note that it says "for hiding" and "when you're hiding" not "for remaining hidden" nor "when you're hidden".
Answer: This can work but is highly circumstantial
In essence I agree with @SevenSidedDie's answer that you must be hidden when you make the attack, however, there is a nuance in the rule on hiding in combat that is being overlooked:

In combat, most creatures stay alert for signs of danger all around, so if you come out of hiding and approach a creature, it usually sees you.

If you come out of hiding and do not approach, say by making a ranged attack, you should get the advantage and all the benefits that flow therefrom. There is a world of difference from knowing the rogue is hiding behind the column and being aware of the exact moment they step out and flick a dagger at you. To rule otherwise is to give the words "and approach" no work to do in the sentence above.
Answer: 5e rules designer Jeremy Crawford addresses this here on Twitter.
The discussion (with a number of different users) starts about using Cunning Action to hide in combat, but gets to answering this question as well. Yes, you can hide in combat and use a ranged attack to get advantage and sneak attack.

need help. If a rogue is in complete cover, can they BA hide? DM rules that enemies are constantly aware despite cover.
The Hide action is one of the actions you can take in combat (PH, 192) because you can, indeed, hide in combat.
as per the rules of Hiding, in combat would the Stealth check be contested by an Active or Passive Perception check?
The Hide action (PH, 192) states that it follows the rules for hiding (PH, 177), which explain the use of active and passive checks.
Issue that came up most often at Winter Fantasy was rogues wanting to always hide around corner, next end move out and attack hidden.
That's a legitimate use of Cunning Action.
When you break cover, aren't you no longer hidden?
If you keep hiding in the same space, I've seen DMs rule disadvantage on the Hide check - like @mikemearls
Or you can have the foes stop falling for it: "Hi there. I've followed you behind this corner."
I am curious: when the rogue starts round hidden behind wall, moves out, attacks... is she hidden during the attack? Or, broke cover and no?
Are you referring to an attack from behind cover, or are you referring to a rogue who moves X ft. in the open and then attacks?
Later. Rogue starts hidden, moves out to see foe, attacks. Players like to argue they are still hidden on attack.
You can attack while hidden and gain the benefit. But if you run out into the open and then attack, you're not hidden when you attack.
my main problem is can a rogue attack with advantage thanks to hiding.
Yes.
say if the rogue has to come from behind corner/tree/cover to get a line of sight, that's ok?
Yes.
Is it up to the DM to set the difficulty or is that always opposed to a perception check?
See "Hiding" (PH, 177) for how hiding works. Unless someone is actively searching, Stealth is opposed by passive Wisdom (Perception).
So shooting a bow while hidden maybe grant the advantage, but running out in melee dont, does that sound about right?
It does!
Comment: Please don't just link to an answer somewhere else because links rot; good answers will bring in the relevant information here.
Comment: The last clarifications clear it up. Stepping out of cover and shooting is still advantage. Running up to someone for a melee is not. Granted, this was before the eratta became the official rules clarifications. I don't know if they touch on these edge cases.
Comment: Agreed, there is an answer above with a link that no longer works, but I couldn't add this link in.
Comment: How do you consolidate "If you run out into the open and then attack, you're not hidden when you attack" with "if the rogue has to come from behind corner/tree/cover to get a line of sight, that's ok? Yes." Am I to understand that "coming out into the open" implies more than just leaving cover and going into line of sight? Does "to come out into the open" mean "to exit the Hidden state", rather than the colloquial "leave cover / enter line of sight"? Previous questions have established that cover/LoS have nothing to do with remaining hidden, but I don't understand "come into the open"
Answer: The Sage Advice segment on the Dragon Talk podcast episode from April 27, 2017 discusses this extensively. Jeremy Crawford goes into substantial depth. The episode is titled: James Haek on D&D Writing. The Sage Advice segment is near the beginning of the episode, a few minutes in.
The ultimate answer is: DM decides.
BUT, the general answer is, it depends on whether or not the rogue is moving. If a rogue can make their attack from where they are hidden, they can then duck back down and try to hide with disadvantage. But if they are, for example, behind a barrel and would have to come out from behind, move thirty feet, then attack, that movement of thirty feet would normally break stealth, so they wouldn't get advantage and the Sneak Attack (SA) from that hide behind the barrel.
Now, the host of the episode asks, what if the enemy is 10 feet away and engaged in doing some other thing? Could the rogue sneak up to the person and maybe make a stealth check (possibly at disadvantage) to see if they remain hidden? Crawford answers, DM decides, as it says in the PHB hiding rules about having a player sneak up on an enemy. 'We built that in because there are too many corner situations.', to paraphrase.
Earlier, he discusses that, if a rogue runs around a corner, hides, and then on the same turn or another, can attack an enemy that is within his range but doesnt have line of sight from behind that corner, that would work. In that situation, the rogue would be an unseen attacker, and would get advantage and therefore SA.
Which, ultimately means, the DM decides. I, as a DM, would absolutely let me rogue/ranger/whatever make a stealth check to move stealthily from hiding to attack an opponent who is otherwise engaged. I would even do it with disadvantage if the opponent wasn't otherwise engaged and was searching for the rogue, depending on how close the rogue was, and other situational factors. The reason is because, even though there aren't facing rules in D&D, it doesn't take six seconds to cover ten feet and stab someone, it takes one or less, and the opponent has to turn around sometime and look a different way if they are searching. But that is MY ruling, and is my privilege as DM. The DM of another game where I play a ranger rules differently, as is his right.
Hope that was helpful.
Answer: Lets break this down into two parts:

Hiding
Sneak Attack

Hiding
A rogue can make a bonus action to Dash, Disengage or Hide (PHB 96).
So, the rogue is in combat, they must Disengage first before they can Hide.
E.g.

Round 1 - Rogue attacks, then disengages
Round 2 - Rogue Hides (IF THEY ARE ABLE TO), then attacks
Round 3 - Rogue disengages, then hides
Round 4 - Rogue attacks, then disengages

In such a way, the rogue is moving in and out of combat, but only able to hide if the terrain provides cover advantage.
Sneak Attack
PHB 96 says that a rogue can sneak attack if they have advantage, or the target is within 5 feet of another enemy of the target (e.g. one of the Rogue's allies, or a stray troll which decided to also attack the Rogue's target), that enemy (the e.g. the Rogue's ally) isn't incapacitated, and the player character (the Rogue) doesn't have disadvantage on attack rolls that round.
A sneak attack is not an attack made from stealth!
Had to repeat that, as this is 5th edition, and sneak attack is different. You can get advantage from being in stealth, but only if the attacker cannot see you when you come out of stealth!

PHB 195: "When a creature can't see you, you have advantage on attack
rolls against it."

A sneak attack is an attack made in combat while the targeted enemy is distracted or cannot see the Rogue and the Rogue has advantage. Remember, each round is 6 seconds long. So, there are many things going on for which the rogue can take advantage. They sneak a jab in here, a stab there, or even an arrow when the target is busy fending off an ally.
Comment: It's just not true that the rogue _must_ disengage before hiding. It might be wise to disengage, to avoid opportunity attacks, but it is not mandatory by RAW. So actually, a rogue can: move, attack, move, and hide, all in one turn; and repeat _ad nauseam_ round after round if conditions allow.
Comment: Adjusted to meet PHB 195 criteria of stealth. Should have done that first. Thanks for pointing it out @Airatome
Comment: Suggest you remove your last paragraph. It defines sneak attack a second time, though you've already done it in an earlier paragraph. Furthermore the second definition does not match the first definition and conflicts with RAW (eg RAW Sneak Attack does not contrast the target's being distracted with the rogue's being unseen and having advantage - which is in itself unnecessary repetition).
Comment: The excessively punctuated, excessively formatted, and excessively repeated line is not required.
Comment: This is assuming a melee rogue. Ranged attacking allows a rogue to just peek around enough to see the opponent and then duck behind cover, all in the same turn. Or if DM doesn't let them repeatedly hide in the same place, they could scurry between multiple sources of cover, if the terrain allows.
Comment: @ClearlyToughpick _Hiding_ "Until you are discovered or you stop hiding, that check's total is contested by the Wisdom (Perception) check of any creature that [searches]." _Unseen Attackers and Targets_ "If you are hidden [...] when you make an attack, you give away your location when the attack hits or misses."  _Basic Rules_ p.74: "You can make an opportunity attack when a hostile creature that you *can see* moves out of your reach." so if you hide -> move -> attack -> move, then you *do not* provoke an attack of opportunity and you end your turn unseen, unheard, and location unknown.
Answer: "Not easily. It can work as long as they avoid being spotted, but not being spotted is the hard part: since the attacker's location is automatically given away and after that it's easy to see them, special precautions are required to prevent being seen despite the target knowing exactly where they are."
PHP p. 177:

In combat most creatures stay alert for signs of danger all around, so if you come out of hiding and approach it usually sees you.  However in certain circumstances the DM might allow you to stay hidden as you approach a creature that is distracted...

Apparently you never spent time in the infantry :)   Being fired upon even with a firearm that makes lots of noise does not automatically reveal the location of a hidden shooter.  With a bow that has minimal noise by comparison, it's even harder.  From a RAW perspective you could stay hidden while shooting (e.g from behind a bush,, or through some narrow opening), or pop around the tree trunk, shoot, and duck back going for another hiding roll since you never approached.  It would take the target of their allies searching for you to locate the source of the attack (taking search action).
Not that this works equally as much for as against the players.
Comment: You seem to be replying to another answer. Please note that answers should address and answer the *question*.
Answer: Posting a side answer to those who seem to vent some frustration at the clause of "A ranged attack reveals the attacker on a hit or miss."
Point A: This was done as a game balancing mechanic that makes a modicum of sense, seeing as you're unlikely to be struck in the back by an arrow or crossbow bolt when the attacker is in front of you. If you get hit in the front, you're pretty positive the attacker is in front of you, and in a position to at least see you, if not be seen by you.
Point B: It also depends on where you're striking from. DM ruling on whether a hidden ranged attacker is covered enough by foliage, shadows, etc. to remain hidden. An archer shooting from a murder hole or a castle crenellation is in an obvious location for a defender to be attacked from, so its highly doubtful you'd receive the "hidden" status from them; whereas shooting from one of fifty bushes/patches of foliage in a dense forest is going to be much more difficult to pinpoint where that arrow just came from.
As a DM, I bow to the rules for reason of balance. Abusing "hidden" to reap additional d6's on attacks just isn't going to happen. Archers should be carefully picking targets anyway; easy shots on the target the party tank has engaged is just much easier than trying to logic bend rules.

The Skulker feat also helps:

Prerequisite: Dexterity 13 or higher
You are expert at slinking through shadows. You gain the following
  benefits:

You can try to hide when you are lightly obscured from the creature from which you are hiding.
When you are hidden from a creature and miss it with a ranged weapon attack, making the attack doesn't reveal your position.
Dim light doesn't impose disadvantage on your Wisdom (Perception) checks relying on sight.
Answer: It can work. Suppose you're not just a rogue, but a halfling rogue and you're shooting. Then you are Naturally Stealthy and can hide when some Medium or larger ally is obscuring you (say, your tank). It's simply a matter of bonus action to hide behind your buddy, roll attack, move if necessary. There may be cover to consider in this scenario. Ranged attacks mean you don't have to go in and out of melee and provoke opportunity attacks (since you're not Disengaging, but Hiding with your bonus action), but cover might apply, even your friend's back.
Now, if you're not a halfling, you need a handy corner, tree, column, darkness spell, or whatever to duck behind.
Note in combat, especially after the first time you try this, your target is likely to have advantage against your Hide check so the difficulty is noticeably higher.
Comment: That allows you to hide, certainly, but how does it allow a sneak attack, i.e. grant advantage? You have to reveal yourself (become visible) in order to get line of sight. Ducking behind an ally doesn't cause an enemy to forget where you are.
Comment: @keithcurtis _Hiding_ "You can't hide from a creature that can see you clearly, and you give away your position if you make noise, such as shouting a warning or knocking over a vase." ... "Until you are discovered or you stop hiding, that check's total is contested by the Wisdom (Perception) check of any creature that [searches]." You do not have to break line of sight to begin hiding, and you do not have to stay out of line of site to continue hiding. Unseen attackers even states "If you are hidden ... when you make an attack, you give away your location when the attack hits or misses."
Comment: Not sure what point you are trying to make here."You can't hide from a creature that can see you clearly" and "You do not have to break line of sight to begin hiding" seem to be contradictory.
Answer: Yes, you can move and attack while Hidden. Attacking will make your location known, but does not reveal you.
First you need circumstances where you can try to Hide:
Hiding

The DM decides when circumstances are appropriate for hiding.
[...]
You can't hide from a creature that can see you clearly, and you give away your position if you make noise, such as shouting a warning or knocking over a vase.

Now you can attempt to hide:
Hide

When you take the Hide action, you make a Dexterity (Stealth) check in an attempt to hide, following the rules for hiding. If you succeed, you gain certain benefits, as described in the "Unseen Attackers and Targets" section later in this section.

Hiding

When you try to hide, make a Dexterity (Stealth) check. Until you are discovered or you stop hiding, that check's total is contested by the Wisdom (Perception) check of any creature that actively searches for signs of your presence.
[...]
Passive Perception. When you hide, there's a chance someone will notice you even if they aren't searching. To determine whether such a creature notices you, the DM compares your Dexterity (Stealth) check with that creature's passive Wisdom (Perception) score

You are now Hidden and thus are unseen and unheard.
Unseen Attackers and Targets

When a creature can't see you, you have advantage on attack rolls against it. If you are hidden--both unseen and unheard--when you make an attack, you give away your location when the attack hits or misses.

You do not have to be unseen AND hidden to get this benefit, being hidden already makes you unseen and unheard.
As an aside, what does "give away your location" mean? The answer is in the preceding paragraph:
Unseen Attackers and Targets

When you attack a target that you can't see, you have disadvantage on the attack roll. This is true whether you're guessing the target's location or you're targeting a creature you can hear but not see. If the target isn't in the location you targeted, you automatically miss, but the DM typically just says that the attack missed, not whether you guessed the target's location correctly.

Now that your location is known, enemies can attack directly at disadvantage rather than having to guess.
The Skulker feat allows you to make ranged weapon attacks without revealing your position (however note that it doesn't work for melee attacks--if you stab someone in the back they know you are behind them):

When you are hidden from a creature and miss it with a ranged weapon attack, making the attack doesn't reveal your position.

So what can you do while hidden? There are only 3 ways for hiding to be removed:

The initial Dexterity(Stealth) check does not beat the Passive Perception check and the character was never Hidden.
An opposing character actively searches for the character and makes a successful Wisdom (Perception) check against the initial Steal score.
The character 'stops hiding' -- you explicitly decide you are no longer hiding.

You can move, dash, cast spells, use items. You will not break your hiding state. However:
Hiding

you give away your position if you make noise, such as shouting a warning or knocking over a vase

For melee attacks:

Hide successfully
Approach your target stealthily
Attack, revealing your location when your attack hits or misses

The character is STILL hidden, but their location is known. If the character ends their turn out in the open (rather than dashing or moving back to safety) then I imagine a perception check (with advantage) would reveal them very quickly!
For ranged attacks:

Hide successfully
Attack, revealing your location when your attack hits or misses

You are now still hidden, but your location is revealed. Luckily you are likely still obscured so opponents probably do not have any benefit to their perception check. Although, with your location known you are vulnerable to indirect attacks, and people coming to check you out!
How do you deal with characters using Hide?

Send someone to flush them out of their hiding place
Use Search to spot them
Ready an action to Search when they attack in melee and are most vulnerable
Ready an action to attack (at disadvantage) their location only once they reveal themselves
Break line of sight with them, make it difficult for them to approach

If you are struggling with understanding the way the game works, please consider these examples:
It is night time, goblins ambush the party by hiding in the darkness. In the gloom the party can't spot the goblins, but the goblins' attacks make their locations known. The party's mage sees an arrow fly out of the darkness and immediately fires off a fireball back at that location.
A thick fog envelopes the party, out of the grey a giant rat jumps out of the fog and bites the warrior's leg, the warrior swings their hammer but the rat has already gone, skittering back into the fog. The warrior looks to the ranger and with a nod the plan is set. Next time the rat attacks the ranger was ready and yells out to the warrior, the warrior swings and catches the rat squarely with a crunch.
The party's rogue dashes out from behind a tree and stabs an unwitting troll. The troll yowls in pain and spins around, but the rogue is already gone--back behind the tree. The troll walks around the tree and sees the now-quivering rogue standing "stealthily" behind the tree.
Answer: This is combat. Realistically if a rogue is firing arrows from a hidden position at a creature currently fighting something else. Their ability to pinpoint an attacker is quite difficult. Especially with how a rogue would build it's gear towards being unseen. Say for instance having a rogue 20 dex and double proficiency has +11 to stealth in 5e with a cloak of elven kind. Is geared for this style of combat. It still require an action to make a perception check even if the location is known. If what your attacking is fighting something in front of it. Obviously the rogue has the upper hand staying hidden.


"Initium doctrinae sit consideratio nominis"

Question: I'm looking for a Latin phrase for starting your exposition by explaining the terms, i.e. its title. I believe the quote is "initium doctrinae sit consideratio nominis," but I'm not sure that that's correct. I haven't been able to find it online, so I'd also like a reference to it in use.
Comment: The current answers provide the source of the phrase you are using, but are you also looking for earlier, native formulations of the same idea in Latin?
Comment: @brianpck Yes, I'd like to have such formulations as well.
Answer: As Joel Derfner points out, the quote comes from the Stoic philosopher Epictetus, and is originally in Greek; it can be found here, in a collection of his sayings by his student Arrian,  in the form ἀρχὴ παιδεύσεως ἡ τῶν ὀνομάτων ἐπίσκεψις. In that text the quote seems to be ascribed by Epictetus to the fifth- and fourth-century BC philosopher Antisthenes, a student of Socrates.
The earliest Latin version I can find is from 1604, in Justus Lipsius's Manuductio ad Stoicam Philosophiam. The Latin translation -- initium disciplinae nominum consideratio -- is presumably Lipsius's own, unless there's an earlier Latin version I've missed.
Answer: So actually your translation isn't correct—or, rather, it's technically correct, but it's not actually correct. I'll explain.
(I should note that this is an edited version of my previous answer—the edits are based on @TKR's comments to this answer.)
The sentence you quote the Latin version of a sentence from the Discourses of the Stoic philosopher Epictetus. The Discourses are transcripts of his lectures, written not by him but by his student Arrian, who wrote in Greek rather than in Latin. Epictetus, however, attributes the sentence to Antisthenes. The sentence means, more or less, "The beginning of education is the consideration [or "the study"] of names."
Comment: The quote from Epictetus is ἀρχὴ παιδεύσεως ἡ τῶν ὀνομάτων ἐπίσκεψις, Discourses 1.17.12, where it is ascribed to Antisthenes: http://www.perseus.tufts.edu/hopper/text?doc=Perseus%3Atext%3A1999.01.0235%3Atext%3Ddisc%3Abook%3D1%3Achapter%3D17.
Comment: @TKR Do you want to write your own answer to this question? I could go back and edit mine to be correct but it would be completely based on the information you gave, and I'm loath to take the credit for your knowledge!
Comment: I've posted an answer, but I was led to the Greek original by your reference to Epictetus, so I think you deserve as much credit here as I do!


instant upload of camera pictures into Google picasaweb without Google+ app?

Question: Is there any option to have instant upload of camera pictures into Google picasaweb without the Google+ app? I have an HTC Chacha 2.3.5 which runs short of memory (even when moving apps to SD), and I can't be bothered of having Google+ installed, but would like to keep the instant upload of camera pictures into Picasa. Right now the Camera app (HTC Version 2.6.2119262927.162876) in the phone can only do instant upload into Flickr or Facebook, but I would rather prefer have them in Picasa. Any ideas?
Comment: Just to clarify, you mean instant and automatic, that is, photo is uploaded as soon as you take picture?
Comment: Yes, I mean instant and automatic
Answer: There is an app for that.
PhotoSync (Sync to Picasa) automatically syncs local folder to Picasaweb, so you can select your camera folder. It's free and not so huge as G+ app. You can set your local folder and Picasa folder and sync them on eg. hourly basis.
Comment: I agree with Tschareck and with @louielouie (below) - a separate app is required, you cannot modify the behavior of HTC's software AFAIK. The choice, then, would be which app suits your needs while taking up the least space.
Answer: I would bite the bullet and install the Google+ app.
In addition to Instant Upload, the Google+ app will give you unlimited storage of the photos that are uploaded via Instant Upload:

All photos uploaded in Google+ will be automatically resized to 2048 pixels (on their longest edge) and won't count towards your free storage quota.

Source: http://support.google.com/picasa/bin/http://picasa.google.com/support/bin/answer.py?hl=en&answer=1224181
I don't think you have to use Google+ other than register online and install the app for this to happen, so there's really not much effort on your part needed to get the benefits of Instant Upload.
You can also manually "share" photos from the Gallery app to Picasa, but that's more tedious.


can you start a new token without smart contracts?

Question: What I mean is, can I start a coin on the ethereum network and distribute the tokens when I want to a set list of addresses?
Answer: Yes you could do this, but you do need a smart contract to handle token logic and also for storage (like storing balances, total supply, etc.).
You could certainly distribute tokens whenever you wanted to whomever you wanted. There is no limit and your contract can do whatever you want as long as you've programmed it to do so.
If you wanted to create tokens for this person, you could do:
function mintToVip(uint _amount, address _vip) public {
    balances[_vip] += _amount;
}

You could also give the total supply of all the tokens to yourself initially then send them to whomever you wish by calling transfer normally:
transfer(_vip, _amount);

Note: the above assumes you are ERC20 compliant.
Answer: A token is usually expected to be a contract with ERC20 functionality from the standard.
But you can create a list of pre-ICO investors, and later assign them tokens when the contract is ready.
Answer: If we use the definition provided by the OED of "A voucher that can be exchanged for goods or services", then sort of.
In order for you to create a token on the Ethereum blockchain, you must have some way of accounting for how many tokens a particular user has; normally, this is accomplished by creating a contract that handles the accounting for the token.
In physical reality, you could put a special sticker on every US dollar bill (or your favourite currency) to turn it into a token for something else. For example, suppose your token was for a pizzeria. All dollar bills with your special sticker could be used as both 1USD OR to get a pizza (which, currently, is probably of greater value in the US).
Unfortunately, you can't attach metadata to individual ether. But you can still do something similar with Ethereum: you could send some number of ether to a particular address that serves as your "genesis address". Thus, being involved in a transaction that originates indirectly from the genesis address can serve as the special sticker. Furthermore, all users of your token would have to create new addresses that only ever receive Pizza Tokens. All ether that can be traced back to a transaction from your genesis address is now redeemable for a pizza. Thus, certain ethereum addresses are now functionally "Pizza Token-only" addresses. Because you're not using the smart contract standard, you'd have to write your own code to ensure that other users don't send ether to their "Pizza Token-only" accounts (thus messing up your accounting system -- you'd void those accounts unless the incoming ether were then sent to another address that you could blacklist as Pizza Token-only). Users would also have to be careful to not mix Pizza Token-only addresses and regular Ethereum addresses. They could run a non-standard wallet to do this. But this is why we have standards -- and the standard requires you to have a contract.
Another weird way of accomplishing this is by mining blocks on the main net and setting your mining node to only include Pizza token transactions. You can then look at the coinbase or the block's extraData to determine if the transactions involved are for Pizza tokens. This, of course, is a very expensive way of issuing tokens if you want to have fast confirmation times.


Where is the setting for metering mode located under the D90 menu?

Question: I own a Nikon D90 Camera. I know that I can select one of the metering modes by using the metering button provided on top of the camera. However, I would like to know under which menu item do these metering modes appear when I click on the menu button located on the back of the camera?
Comment: Check the camera manual. All menu options are listed there. Intuitively, it should be called 'Metering'.
Comment: This seems like one of those questions where the *real* question is disguised.  Since you know a quick and easy way to change it with the button, why do you want a menu option?
Comment: @ahockley: There are some people who are curious to know things that are not documented well. I am one of them :-)
Answer: No, you cannot change the metering mode via the menu.  You can't change exposure compensation, shutter speed and aperture, and most other things that have special buttons or dials setup for them.
The menus are more for specialised and detailed settings.  For example there is a dial for setting the self timer on/off, but a menu option to set the self timer delay and number of shots (which has many choices unsuitable for a simple dial).  There is a button/dial for white balance, but a menu to fine tune the white balance presets.  And so on.
Most anything you might need to frequently change has a convenient button or dial, and litte or nothing is then duplicated in the menu.
Answer: Thought this would be easy...  press Menu, scroll up/down the left hand column to "CUSTOM SETTING MENU", press OK, scroll up/down to item (b) Metering/Exposure, press OK...  and it's not there!
I believe I have just gone through all the menus and couldn't find it, is that possible?  Maybe you can only change the metering mode via the dedicated button and the scroll wheel?


creating an array from the value of a single cell in excel

Question: I have a spreadsheet where I want to have:
1) A source cell, which will have a string such as D2594D8-8.
    You can see this is a string of hexadecimal digits without a delimiter except the single dash
2)a group of label and "target" cells where a macro will copy each individual hex digit from the source cell individually.
So an example would be:
Step 1: Enter into D1 the value: D2594D8-8
Step 2: Run the macro
Step 3: the values of the cells:
    C4 updated to equal "D"  (The first character from the source cell string)
    D4 updated to equal "2"  (The second character from the source cell string)
    E4 updated to equal "5"  (The thrid character from the source cell string)
     etc....
I currently am trying:
Sub AssignData()

Dim wldData As Variant
UWParray = Array(Range("D1"))

Range("D4").Value = UWParray(0)
Range("D5").Value = UWParray(1)
Range("D6").Value = UWParray(2)
Range("D7").Value = UWParray(3)

End Sub

But that only gets me:
    "Run-time error '9'
    Subscript out or Range
and the result:

1  D2594D8-8
  2
  3
  4
  5
  6
  7

Any help would be appreciated!
Thanks in advance
Comment: You asked for C4, D4, E4 etc in your text, but your code attempt is D4, D5, D6 etc?
Answer: Your code is taking the entire D1 value and putting it into the first position of the array, so when it goes to look for the second position, it doesn't exist--hence the "subscript out of range" error. The below code works.
    Sub AssignData()

Dim wldData As Variant
Dim UWParray() As String
Dim i As Integer

ReDim UWParray(Len(Range("D1").Value))

For i = 0 To Len(Range("D1").Value)
    UWParray(i) = Mid(Range("D1").Value, i + 1, 1)
Next

Range("D4").Value = UWParray(0)
Range("D5").Value = UWParray(1)
Range("D6").Value = UWParray(2)
Range("D7").Value = UWParray(3)

End Sub

Answer: A one liner :)
[c4].Resize(1, Len([d1].Value)) = Application.Transpose(Evaluate("=index(mid(D1,ROW(1:" & Len([d1].Value) & "),1),)"))

Answer: This should do what your asking:
Dim my_array() As String
Dim my_String As String
Dim i As Integer

my_String = Range("D1").Value

'Replace "-" with nothing
my_String = Replace(my_String, "-", "")

'Split my string into individual characters and store in array/worksheet
ReDim my_array(Len(my_String) - 1)

For i = 1 To Len(my_String)
    my_array(i - 1) = Mid(my_String, i, 1)
    'Store values in excel sheet starting at C3
    Cells(4, (2 + i)).Value = my_array(i - 1)
Next

You actually don't need to use an array to store the values into the worksheet's cells, but I added it because of the post title.


Teamcity nuget feed http authentication

Question: Nuget feed by team city  is working perfectly but there is a strange problem.
Local IP (http://192.168.xx.xx:9999/feed/../):
Listing through browser works
Accessing packages  through Visual studio 11 nuget works
VPN IP (http://55.xx.xx.xx:9999/feed/../):
Listing packages through browser works
Accessing packages  through Visual studio 11 nuget PROBLEM
GUEST Account:
Everything works fine, both on VPN and local IP (so its purely an authentication problem)
The problem is, we can't get the user to authenticate. Using the same credentials, no matter what we try we get 401. The server VPN ip is whitelisted in internet explorer intranet settings. Any ideas? Basically HTTP authentication is failing for the VPN although it shouldn't, since the browser works fine!
Answer: I think it has something to do with TeamCity thinking the server is called X and doesn't recognise the alias Y.
In my case the DNS CName didn't work, but the correct name did

Teamcity nuget feed http authentication


What are the major criticisms of Alain Badiou's claim that mathematics is ontology?

Question: Building on Was mathematics invented or discovered? I would like to know what the major criticisms are of Alain Badiou's claim that mathematics is "the very site of ontology" (in Being and Event.)
Answer: It seems to me that Badiou is himself providing the criticism or response, specifically to theorists like Heidegger and Deleuze. I'm not sure anyone has published any major criticisms of his arguments. In a way, he's attempting to rescue the idea of objectivity, to rehabilitate truth and the notion of the subject, from the ontological criticisms set forth by the theorists who came before. It's a breath of fresh air for those who think of Deleuze as a "dead-end", not necessarily to be read as a contradiction of that work.
The specific criticisms, as I understand them, would probably go something as follows:

Badiou continuously ignores and even refuses to recognize the "suppleness" of power, and its effect on the discourse of alterity. He says that the association of pathos with these forms of alterity is both disruptive and unnecessary, and even attempts to remove alterity and pathos from the equation entirely through the use of mathematical axioms, but this is impossible. Despite the claims made in his works, he is still haunted by an "ineradicable remainder of pathos". Here, you can read the entire earlier works of Emmanuel Levinas (to which Badiou is responding) as themselves indictments of Badiou.
Slavoj Žižek is also a critic in some senses (though he possesses an extreme amount of respect for Badiou's thought, describing him as a "giant who walks among us" and likening him to Plato or Hegel), with the primary point of divergence being Žižek's allegiance to Kant and Hegel, contrasted with Badiou's rejection of both. Žižek is very much on the side of "finitude", whereas Badiou attempts to overcome the very problem of finitude. In particular, though Badiou accuses the philosopher's "denial of enjoyment" as making her vulnerable to asceticism, the philosopher can in turn accuse the psychoanalyst (Badiou) as being transfixed by his own enjoyment, particularly since Badiou's argument is that contemporary culture exists almost entirely "under the emblem of enjoyment". Specifically, Bruno Bosteels makes this observation in an article he contributed to Alain Badiou: Key Concepts, edited by Bartlett and Clemens. (Although Bosteels is attempting to clarify and synergize the works of the two theorists, rather than strictly offering a criticism of Badiou.)
Gilles Deleuze (and, to a lesser extent, his good buddy, Félix Guattari) is probably Badiou's primary antagonist. Although both interpret philosophy as involving the thinking of the multiplicity, Deleuze stubbornly refuses to give in to Badiou's willingness to cede the thinking of enjoyment to the psychoanalyst. The primary author to consider here is Deleuze's student and contemporary, Eric Alliez. Suggested readings might include his essay "Badiou: the Grace of the Universal" and his contributions to the above-suggested title, Alain Badiou: Key Concepts.
Giorgio Agamben also opposes Badiou in his insistence upon the "irreducible remainder". In essence, he argues that the ethic of truth proposed by Badiou actually requires the "occlusion of the remainder", and Agamben's entire understanding of philosophical discourse rests on the potentiality of the remainder, primarily through his central concept of "bare life", which can be interpreted as life which is resting on the very verge of death.
Comment: It would be nice, given the question, if you called out what any of this has to do with mathematics.  (or Joseph should make the question itself more open-ended.)
Answer: I think it's worth reading the critique by Ricardo L. Nirenberg and David Nirenberg on Badiou's maths. They fundamentally claim Badiou's equation 'ontology is mathematics' is reductionist. Look for the whole exchange as Badiou's reply is also worth reading not for the quality of the reply but for the violence and lack of academic respect in the debate. The exchange is in the journal Critical Review.


Long boils are ruining enamel on stove, is there any way to prevent this?

Question: I have tried putting aluminium foil about 3 inches out from around burner, but that seemed to exacerbate the problem. I think it helped the insulate the area under the foil.  It seems like I am ruining the stove.  Is there anyway to prevent this from happening?  I know I can get a burner for outside, but I would really rather brew inside the house.  Especially in the winter.
Answer: There is some experimentation going on with immersion of water heater coils for boiling, but I have no experience with that.   I hear that it's fast and efficient, but I would be nervous about water + high voltage.
Comment: I wouldn't call it experimentation.  Many brewers have been doing it that way for a long time.  Its perfectly safe as long as you take the right precautions.  We take precautions with the propane and natural gas set ups most of us use, and I view that more dangerous than the electrical setups.
Comment: Ah, experimentation. Space age technology.  Turns out, tens of millions of people have been "experimenting" with these since as early as the 1860's to heat the water they bathe in.  In any case, it's discussed in more depth in this thread: http://homebrew.stackexchange.com/questions/2677/how-to-brew-all-grain-indoors
Comment: Yes, I would have the same worry.
Answer: I think the answer to this question is that I buy a burner and do the brewing outside.  Its not perfect and does require some more $, but its an imperfect world and given that I live in Florida, I can brew outside year round.  I will just have to watch the forecast for rain.
Answer: I'm a little late to this question, but I thought one solution might be to put down a layer of fiberglass fabric, the kind that is impregnated with epoxy to form fiberglass hulls and such.  In its fabric form it is easy easy to lay down underneath and around the burner, non-conductive (if you have electric burners), impervious to heat, and an excellent insulator that should block most of the radiant heat coming off the burner.
Answer: I wonder if this foil insulation would help: http://www.lowes.com/pd_13353-56291-ST16025_4294858104_4294937087?productId=1014123&pl=1&currentURL=/pl_Foil%2BInsulation_4294858104_4294937087_  It seems like you could just lay a sheet over the enamel while you boil.  Of course, the first time you use it, you should probably babysit it to make sure it doesn't catch fire!


How do I view all shares of my posts?

Question: On my Facebook page it tells me I have had 11 shares.  There is a link to view all shares.  I click on this link and I only see 2 shares.  Why am I seeing only 2 out of 11 shares?
Answer: You can only view the shares that you have access to - that is, shares by your friends, or shares which are public.
I believe in testing, page admins could see all of the shares of their content, but this has been locked down.

How do I view all shares of my posts?


Should I use gyro or encoders for robot moving in straight line?

Question: I've recently succeeded in building my first collision-avoidance Arduino robot with 2 DC motors, and it works pretty well. However, it doesn't move in a straight line yet, when it should. I'm now studying which method should I implement to make the robot go straight. I've heard about using IMU or encoders with feedback control. I pretty much understand how to use the encoders, but I'm not sure about the gyro. Should I use just one of those or a combination of them?
Answer: The problem here is that you are trying to drive in a straight line without any external reference. Wheels slip (making encoders give error), gyro's drive (so there's error there to), magnetometers have issues with nearby magnets, and GPS may not work on the scale you want it to. So what are we left with? Sensor fusion.
If we use a combination of an encoders (to measure the actual wheel speed) with a gyro (to measure the short-term rotation changes), with a magnetometer (to achieve long-term direction management).
Hang on, this is getting expensive and hard. How long did you want to drive in a straight line for? 1m, 100m, 100km? What terrain. If it's a tabletop, encoders or a gyro would work. If it's off road, you need more.
Encoders
An encoder gives ... rotational velocity of the wheel. You can integrate this into rotational angle of the wheel to determine how far you've moved. You can compare this with the other wheel's distance to figure out whether the robot has rotated. At high speeds, you need to poll the encoder really fast, or set up interrupts.
Gyro
Don't ask me how a solid state gyro works, but it gives you the rotation change of the robot directly. Unfortunately, this include the rotation of the earth, and so gyro's drift over time. In my experience, with a small RC car-sized robot over ten minutes, the drive of even a cheap gyro is negligible. Once again you're integrating though, so you have to poll it quite fast, and most gyro's talk over i2c, which can be a bit of a pain.
Note that the accuracy of a gyro depends on it's mounting as well. If it's subject to lots of vibration, it will drift faster.
Magnetometer/compass
With some soft iron, you can shield them from your motors just fine, and they provide and absolute orientation relative to earth. Sounds great? Yup, worked fine one one of my robots, but on the competetion day, someone else had three magnets capable of lifting 25kg each. My robot went into orbit around it.
But, if you can ensure that there aren't going to be massive magnets near your robot (other than the robots own motors, which you can shield and then calibrate out to some extent), you can get ~2-3 degree accuracy with very little effort.
Fusing
If you spend a couple more dollars, you can find a 10DOF board that includes a gyroscope, magnetometer (and accelerometer and barometer). Then you can apply some sensor filtering to combine the long-term accuracy of the magnetometer (assuming you drive past the magnets) with the short term (ok, ten minutes or so) sub-degree accuracy of a gyro. Where did the encoders go? Well, I tend to deal with vehicles with tracks (which slip) or offroad (which slip), so I haven't worked with encoders as much as the others.

The physical device that I use in my hobby projects is the GY-87 10DOF board, which uses the MPU6050 accelerometer-gyro and the HMC5883L magnetometer. You speak i2c to the MPU6050, and the MPU6050 can speak to the HMC5883L for you.
Comment: Fusion is the best way to go for sure. I've got only one concern about encoders' output: normally, they provide position feedback. Hence, the corresponding velocity needs to be estimated somehow. This task could be easy with high (thus expensive) resolution encoders and simple differentiation, or tougher with state-space or SG filtering.
Comment: It all depends how accurate you need to go. If you have a 1024 tics per rev encoder and a 5cm radius wheel you get an accuracy of 0.3mm. A cheap $4 encoder is 24 pulses, or about 1.3cm. So you use a smaller wheel or measure before gear reduction. And to go from the tics of an encoder to a position or velocity isn't actually very hard. I've yet to meet something that standard quadrature decoding didn't work fine for.
Answer: Either is going to require feedback control (PID or some subset thereof) to function correctly. I personally have had the most success with encoders, however, I haven't spent a ton of time with accelerometers, but I would assume unless you have an accurate one it may be kind of a pain. Encoders are usually built into motors and are fairly idiot proof.
Answer: There is no good substitute for knowing exactly what your wheels are doing. Even with a gyro, you may not get a straight line, as all gyros have drift (and the ones with low drift are expensive). Also, a gyro won't allow you to accurately control wheel speed and won't tell you when a wheel is slipping or stuck. Encoders will buy you much more than a gyro.