Why are calculator and phone number-pads different? Gavin Evans
I don't think anyone knows for sure. However, adding machine and calculator keyboards have had 789 across the top for as long as I can remember, which predates electronic calculators. Phone companies started with 1 at the top of the dial, and their push-button phones started with 123 at the top. I suspect it's just different industries with different traditions. For more information, see www.vcalc.net/Keyboard.htm.
Backchat: Roy Wilson says: "The Post Office Engineering Department (pre-BT) used to test everything about the telecom system" and "the 123 layout produced the least errors". Bev Pease says that in the US, "the Bell Labs folk, and others, did huge amounts of research" with the same result. Andrew Emmerson notes that desktop calculators and adding machines "were used by skilled clerks often called comptometer operators" and the "adding up" keypad layout was very efficient for them. However, "human factors tests with all manner of different keypad layouts proved repeatedly on both sides of the Atlantic that the 'counting down' scheme pleased telephone users best".
