Keyboards that have a variety of functions for each of the different keys are relatively uncommon. But these often exist as part of the more traditional keyboard (for example, the top row of keys on the keyboard). Keyboards with a variety of functions per key are often particularly useful in process industries. A common form is to have a row of unmarked keys under the monitor screen, and to have squares representing the different keys directly above them on the screen. Depending on the picture being shown on the screen, text appears in different windows showing the functions that the keys have for each frame. There are more advanced systems for this type of keyboard where there are several rows of unmarked keys, and parallel pictures are projected down from the screen onto the keyboard using an arrangement of mirrors in order to show the current function of the keys. Because considerably fewer keys are used on this type of keyboard, fewer hand and arm movements are required by the operator. This reduces the risk of errors occurring.
Another application for this type of keyboard is to build lights into the keys. The relevant keys light up for each particular function. The lights in the keys are illuminated or extinguished when particular keys are pressed, depending on the sequence of operations required. In this way the operator is guided through the correct operation sequence. Nonilluminated keys are then disconnected from the system. The risk of errors occurring with this type of system is very small, and work on this keyboard is also faster, particularly if the operator is not accustomed to the work. It is important, however, that a warning signal is produced if the lights in the keys fail.
There are also applications where keys can be pressed with different pressures. A soft (gentle) pressure on a key causes the function associated with that key to be displayed on the screen, and the action is taken if the key is pressed harder. If it is fully depressed a signal is sent to the computer dictating changes to be made to the process. The operator can also receive new information on the screen that informs him which new keys can be used.
Depending on its design, the keyboard can be preprogrammed to lead the operator naturally through the work. This type of programming of the keyboard functions may be an advantage for especially important types of operations, where errors could have serious consequences. From the perspective of the operators, a major disadvantage is that they may feel their work is being too highly controlled. Another disadvantage with this type of keyboard is that it requires a lot of programming, and this takes up a large part of computer capacity. An advantage is that the hardware does not need to be changed (rebuilding or extending the keyboard, or other changes) to any great extent even if a major change is to be made in the function of the controls. In other words, this form of control is very flexible. Keyboards can also be adapted to people with specific handicaps such as Braille scripts for vision-impaired people or special large keys for people with motor deficiency.