789 or 123

Ever wonder why keypad layout is different between phone and computer/calculator?

I guess when you have to combine number and alphabet in a single button, Bell Lab had to go with top down option. And the buttons on the phone are intentionally smaller and spaced out to decrease human factor error also. Thanks to The Bell System Technical Journal (July 1960 issue) touchtone_hf.pdf (630.95 KB) an amazing amount of research was conducted. Now devices like microwave, remote control, ATM are designed the same way as phone keypad. As for the calculator, it could work either way but the bottom up layout seems faster to punch in a lot of numbers.