History of 十干（じっかん）and modern uses


As I was studying vocabulary today, I happened to come across the titular 十干
which are as follows:

> [甲]{こう} • [乙]{おつ} • [丙]{へい} • [丁]{てい} • [戊]{ぼ} • [己]{き} • [庚]{こう} • [辛]{しん}
> • [壬]{じん} • [癸]{き}

There's a somewhat lengthy definition near the middle of [this
page.](http://ginjo.fc2web.com/117obikyuu/obikyuu.htm)

I happened across this while looking up the word へい（塀 - wall), and the first
entry in my プログレッシブ dictionary was 丙（へい）- showing the definition as "3rd rank"
or a "grade of C (in school)". I proceeded to find that 甲 and 乙 are also used
to mean a grade of A and B respectively.

My questions are:  

  * Are these used in modern Japanese for ranking things??? If so, all of them, or just like the first 3??? And what kinds of things are ranked this way???
  * Is this a part of 尺貫法 or is it something completely separate???

_[Side note: would anyone be interesting in making/helping to make a community
wiki on 尺貫法? I find it strangely fascinating for some reason.]_




I use 甲 and 乙 when writing business-to-business **contracts** , meaning first
party, second party.

