 keys which can be programmed for special functions. The screen cursor points to the position on the screen where the next character will be displayed. Cursor movement can be handled man- ually from the keyboard or can be under program control. Normal cursor movement is up, down, left, right and home. Some terminals also provide protected fields and scrolling. Pro- 54 TELECOMMUNICATIONS tected fields are used to retain certain data fields which are used re- petitively. For example, a protected field would be a title such as name, address, etc., after which the operator enters information. When the transmit key is depressed, only the variable data is trans- mitted. Most terminals provide a scrolling function. Scrolling allows the operator to roll page information retained in a scrolling buffer back onto the screen where it can be checked or modified. 4.1.3 Display Schemes Most terminal displays are cathode-ray tubes (CRTs) which employ a dot matrix to form the character. The screens are rectangular with their measurements given in diagonal inches. Screen sizes vary from a few inches to about 15 inches. The screen's capacity is the maxi- mum number of characters that can be displayed at one time. Most manufacturers have standardized on 1920 characters which is derived from a format of 24 lines by 80 characters per line. An increasing number of vendors are also offering 132-character-per-line displays. This corresponds to a typical computer printout, and can be used to check format. Of course, the more characters displayed per line, the harder it is to read. 4.1.4 Terminal Considerations There are two conflicting interests and tradeoffs in terminal selec- tion; namely expense verses line utility. Most low-cost terminals are start-stop, with no buffers. Buffered, synchronous terminals are more expensive but give better line utilization. Where the lines are short and inexpensive (e.g., within one city), efficient line utilization is of little importance. When a dial-up line is used, normally there is only one terminal