It seems to me that the true "proficiency" of each key that a person types on a keyboard is not accurately measured by just the percentage of correct keystrokes. I can guarantee close to 100% accuracy by taking as much time as I need to find the right key. The standard typing test practice of subtracting errors from overall words per minute (WPM) is also a very crude measure. It seems to me that to get an accurate proficiency rating for each key, I would need the percentage correct and the time interval from the previous keystroke. Suppose I have a program that will give me a string of text to type and will record both the accuracy of each keystroke and the time interval from the previous keystroke (in milliseconds). And suppose I get this data for 6 of the keys: Code: C/R C D E F G H I 5 Key 1 2 3 4 5 6 6 %Correct 0.99 0.99 0.95 0.95 0.90 0.90 7 Interval (ms) 200 300 200 300 200 300 8 WPM 60 40 60 40 60 40 9 Proficiency ??? ??? ??? ??? ??? ??? How do I combine rows 7 and 8 to get a relative proficiency for each key (row 9)? Is key #3 (Col F) with an average accuracy of 0.95 and an average interval of 200 ms (60 WPM) more or less proficient that key #2 (Col E) with a higher proficiency (0.99) but a slower speed (300 ms = 40 WPM)? Any suggestions?