Performance on a prototype keyboard with ternary chorded keys.
Ten subjects learned to operate a ternary chorded keyboard which took them, on average, just over three hours. After an additional 10 h of use, they were inputting an average 70 characters/min with an accuracy of better than 97%. The individual performances were quite different and variable, but throughout rapidly improved. The experiments indicated that people are able to memorize 59 chords, and to execute them quickly, with surprising facility.
Kroemer
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Industrial Ergonomics Laboratory, Human Factors Engineering Center, Industrial and Systems Engineering Department, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061-0118, USA.