Why is a Calcs keypad upside down when compared with a telephone keypad?
The bottom row of Calc’s keypad is numbered 123 with 456 and 789 above, like all calculators. A telephone keypad has 123 at the top with 456 below and 789 below that. In both cases the zero and other buttons are on the bottom row. In around 1960 the telephone companies apparently arrived at their keypad layout as a result of useability research. It probably also made more sense to run the numbers top to bottom because of the alphabetic groups (1=ABC, 2=DEF, etc.) which would suggest reading left to right and top to bottom. The early mechanical adding machines had a set of number buttons for each digit, e.g. the comptometer, and these ran from 0 (if used) or 1 at the bottom to 9 at the top. This was probably easiest for the design of the adding mechanism. When the first “ten key” calculators were manufactured they probably just extended the same convention for the smaller keypad. As usually happens with these things, once the standard is established there is no incentive for anybody to
