The VisionKey ABC character chart shows 49 keys in a square 7 x 7 arrangement which subtends about 26 degrees to the eye. This gives a total of 147 possible selections, a number which allows every computer keyboard key to be allocated. The Command case accesses all the computer keys such as the F1 to F12 keys, Insert, Home etc. The keychart characters are grouped in blocks of four keys occupying top left, top right, bottom left and bottom right positions. At any one time, the user can select from no more than 16 positions, each corresponding to a block.
Similar remarks apply to characters located at other positions in the block.
During selection, when the eye is steady, the selected key becomes highlighted. This confirms to the user that the machine is following the eye. After the user has become familiar with the keychart layout, an operating speed of about 1 character per second is achievable. Field experience With users and trials in over a dozen countries, a wealth of experience has been amassed with a variety of disabilities. As a result, various improvements and new features have been added both to the equipment and to the fitting, training and support processes.