I just noticed my external USB numpad has 7–8-9 on the top row while my phone dialer puts 1–2-3 up there — why do we do it that way? Is it just adding-machine legacy or something from Bell Labs tests, and does it help with data entry speed?
Short answer: calculators inherited 7–8–9 on top from adding machines, but Bell Labs human‑factors tests in the 1950s (Karlin et al.) chose 1–2–3 on top for phones because novices made fewer errors and learned it faster; speed was otherwise similar. If it keeps tripping you up, you can remap a USB numpad to phone layout with AutoHotkey or use a dialer app that mimics calculator style — two tribes, same digits. Source: Telephone keypad - Wikipedia.