Why are numbers arranged differently on keypads and calculators?

Q: Why are the rows on a calculator or number keypad arranged with the lowest numbers at the bottom when we normally read from top to bottom? And why are phone keypads arranged with the lowest numbers at the top?

A: Mechanical adding machines, based on rotating wheels, always have the ‘0’ button adjacent to the ‘!’ button.

By convention, most old adding machines had the numbers increasing in value from the bottom and this may be a hangover from when the machines had levers on the wheels rather than buttons.

When the numbers were put onto a pad arranged as a three by three grid with one left over, the order of the numbers, as far as possible, kept the same, according to a report in New Scientist.

On a rotary telephone dial the ‘()’ comes adjacent to the ‘9’ because a ‘()’ in the telephone number is signalled by ten pulses on the line.

When telephones acquired push buttons in a grid the ordering of the buttons was carried over from the old telephone dial.