Calculator vs. telephone keypads


I have a question: Does anyone know why the keypads on a calculator and a telephone are arranged differently? Please e-mail me the answer if you know it!
Many thanks,


This bit of trivia is in this site's FAQ


As far as it goes in the UK (I don't know about the US) the reason that '0' is near the '9' is the way older phones indicated the number to the local exchange.

Each number was associated with a number of 'clicks' on the line. '1' = one click, '2' = two clicks etc. up to '9' but '0' was ten clicks. On rotary dial phones there was simply a number of notches behind the dial (0987654321) so the further you turned the dial the more clicks were applied to the line when it rotated back to the start position. These clicks were decoded at the exchange as the number you wanted to dial.

Occasionally due to noise or someone wiggling the wires a click could appear on the line when you were not dialing. These errors could upset the phone system and that is why numbers did not usually start with '1' or '2'. It is also the reason why the emergency number is 911 (999 in the UK but 911 also works here) because 9 clicks would not occur very often due to noise and hence the emergency services would not have loads of false calls.

When DTMF (Dual Tone Multiple Frequency) was introduced the tones were 'laid out' using the familiar 123,456,789,*0# format. (It's a bit difficult to explain here but each tone was associated with a column and row and pressing the button closed switches which generated the required tones. A bit like the key codes for HP calcs - row/column, 4 rows and 4 columns on the phone giving 16 tone pairs - only 12 are used on most phones - I think the other 4 were reserved for special users in the US (telephone companies and military?)

Anyway to get back to the question:

Calculators have '0' meaning zero but on telephones '0' realy means ten so it was near 9 for the above reasons.

Why telephones start with 1 at the top is still a mystery to me. One thing I heard was that the telephone companies did NOT want people dialling too fast with DTMF so laid the numbers out in an unfamiliar format to slow people down!

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