Recently, I watched this video by Guy Dupont on building a physical version of the T9 keyboard used on feature phones:
In it (at 2:09), he explains that one advantage of a T9 keyboard is that the ratio of keystrokes:characters typed is reasonably close to 1:1 (about 1.07 keystrokes per character according to MacKenzie, I. S. (2002)).
This got me wondering: could we rearrange the letters on a T9 style keypad to further reduce this ratio?
T9 is a type of keyboard software used on feature phones (phones with a 0-9 keypad) to allow easy typing of text messages.
To type on a T9 keyboard, you press the buttons corresponding to the letters you would like to type, and the predictive text algorithm will present the most likely interpretation of your keypresses.