umbersome. Different systems provide different information in the display. Some show the date and time when the telephone is not in use. Some provide instruction prompts to the person attempting to use sys- tem functions. Most show the name or extension number of the person calling you, if the call is coming from some- one else within your office. Some show the name or telephone number of the person calling you from another location (known as Caller ID or ANI - automatic number identification - if this information is being delivered to your PBX over your outside lines.). A few systems enable you to leave a pre-selected message SO that when some- one calls your telephone from within your office, his 8 $ The Telecom Handbook CHAPTER 1 display will read that you are "out to lunch" or "in a meet- ing." Other systems enable a secretary to send a silent message to the boss while the boss is on another call, al- though this is not common. As with the feature buttons, the important thing to remember is that telephones and telephone systems from different manufacturers use the display differently. No two are exactly the same. g. Lights (also called lamps or LEDs - light emitting diodes) On some systems there may not be a light, but an LCD (liq- uid crystal display) indicator instead. Most people find the lights easier to see than the LCD. The purpose of the light or LCD is to indicate the status of a call in progress on one of the outside lines or extensions. The light may be red, green, white or amber and more than one color may be lit at the same time. This differs considerably depending upon the manufacturer and model of the system. A light flashing on and off slowly may indicate a new incoming call and is some- times accompanied by an audible ring. If the same extension appears on more than one telephone it may simply flash at some telephones and audibly ring on others. A steady light usually indicates that the line is in use on either your tele- phone or another telephone that picks up the same line. A rhythmically f