By the way, if anyone is trying to design a number pad or calculator keyboard or similar for personal use with the goal being comfort/speed after retraining rather than prior familiarity, I’ve found it works much better to put two numbers on each finger.
This is much better (faster, more comfortable, fewer errors) in my experience than the number row at the top of a keyboard, or a standard 3x3 + 1 grid calculator, computer, or phone keypad.
Something along the lines of http://i.imgur.com/ofeQEC9.png
This is much better (faster, more comfortable, fewer errors) in my experience than the number row at the top of a keyboard, or a standard 3x3 + 1 grid calculator, computer, or phone keypad.