Appl Ergon. 1992 Apr;23(2):83-90. doi: 10.1016/0003-6870(92)90078-a.
Applied ergonomics
K H Kroemer
PMID: 15676852 DOI: 10.1016/0003-6870(92)90078-a
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.