They should have a minimum diameter of 7.5 cm. As well, gliding touch pads are available which are activated by the movements of the finger. The advantages and disadvantages of these various input devices have not been well studied, and should be experimented with before purchase. Wrist Support Foam pads placed in front of the keyboard known as wrist supports remove sharp, uncomfortable edges. These are recommended for frequent VDT users.
Wrist supports tend, however, to be misused.
Wrists should only be rested on the wrist support during pauses in keying and should not be rested on the wrist support while the user is typing. Copy holder Copy holders are recommended for individuals who perform input tasks from a source document. Copy holders eliminate frequent neck movements caused from looking back and forth between screen and paper, as well as continuous refocusing of the eyes. To maximize the benefits of a copy holder, it should be at the same height as the monitor, and as close to the monitor as possible. Lighting The recommended luminance at a VDT task area where data entry and retrieval is performed exclusively is 750 lux.