Less well remembered is the companion device, seen in a few of the pictures, with 5 piano-like keys for your left hand to rest on. The idea was that you could

Less well remembered is the companion device, seen in a few of the pictures, with 5 piano-like keys for your left hand to rest on. The idea was that you could “play” 31 different “chords” instead of typing on a keyboard (with some sort of “shift” chord to get numerals and punctuation; or maybe a foot-pedal?). The huge advantage was that you never had to move your hands between the mouse and keyboard, and have to re-find the home row, etc. I saw a number of people actually using this system, including support staff, during a visit to SRI around 1980. Speed and accuracy were reportedly stellar; the downfall, evidently, was that everyone developed Repetitive Stress Injury from chording (before RSI was even a thing).