Why is the telephone keypad opposite the calculator keypad?

Posted by Devin Miller on February 19, 2018

Opposites attract but why are they opposite?

A calculator keypad and a touch-tone telephone keypad have the exact opposite layouts. Here are the top theories for why the keypads are different.

The telephone's circuitry and tone-recognition hardware.

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 personnel who used calculators fairly regularly were adept at navigating calculator keypads. They could hit the keys quickly, which was great for data entry but not for dialing a touch-tone phone. The tone-recognition technology could not operate at the speeds at which the data-entry personnel could dial the numbers. The telephone designers reversed the layout of the telephone keypad to decrease dialing speeds and enable the tone-recognition to work more reliably.

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1960s Bell Labs Study

This study involved testing different telephone-keypad layouts to identify which keypad layout was easiest to master. After testing several layouts, it was determined that a three-by-three matrix with 1, 2 and 3 across the top was the easiest for people to use. Other layouts that were tested include one that used two rows with five numbers each and another that used a circular positioning,

Rotary Telephone

On a rotary dial, the 1 is at the top right and zero is on the bottom. Because Western writing is read from left to right, when designing the new touch-tone keypad, putting the 1 on the top-right didn't make sense. Putting 1 on the top-left and the subsequent numbers to the right made sense. The resulting rows fell into place with zero getting its own row at the bottom.