Why calculator and telephone have a opposite key layout to a computer numeric keypad?

Have you ever thought that why a calculator and a touch-tone telephone have a opposite key layout to a computer numeric keypad?

I tried to investigate the reason behind this. I don’t have the correct theory but a few theories exist.

The first theory is that When the touch-tone telephone was being designed in the late 1950s, the calculator and adding-machine designers had already established a layout that had 7, 8 and 9 across the top row. Data-entry professionals, and others who used calculators were quite habitual at navigating these keypads. They use to hit the numbers extremely quickly, which was great for data entry, but not so great for dialing a touch-tone phone. The tone-recognition technology could not operate effectively at the speeds at which these specialists could dial the numbers. The telephone designers figured that if they reversed the layout, the dialing speeds would decrease and the tone-recognition would be able to do its job more reliably. This theory has little proof to make it reliable, but it does make sense.

A second theory refers to a study done by Bell Labs in 1960. This study involved testing several different telephone-keypad layouts to find out which was easiest to master. After testing several layouts, including one that used two rows with five numbers each and another that used a circular positioning, it was determined that the three-by-three matrix that had 1, 2 and 3 across the top was the easiest for people to use.

Another theory is based on the layout of a rotary telephone. On a rotary dial, 1 is at the top right and zero is on the bottom. When designed the new touch-tone keypad, putting the 1 on the top-right didn’t make much sense, because Western writing is read from left to right. But putting 1 on the top-left, and the subsequent numbers to the right, did make sense. Using that formula, the resulting rows fell into place, with zero getting its own row at the bottom.

All of these theories are there to explain why telephone and calculator keypads are exact opposites, but none of them can be pinpointed as the actual reason. It is common practice today to use the telephone-keypad layout when designing new products that utilize a keypad, such as ATMs.

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