Have you ever noticed that the keypads for calculators and phones are different? Though both keypads have zero at the bottom, the remaining numbers go from bottom to top on the calculator, and top to bottom on the phone. Why is that? Read on to know.

The story begins back in pre-calculator days, when there were mechanical cash registers. These cash registers were designed with 0 at the bottom, and the numbers going up. While making numerous calculations, 0 is the number which is used the most. So it made practical sense to place it below all other numbers so that it is the most accessible. When mechanical calculators made their appearance, they used the same format as cash register with 0 at the bottom and 9 on top.

When electronic calculators were invented, they implemented the keypad arrangement of the existing calculators. 0 at the bottom, 1-2-3 in the next row, 4-5-6 in the next row, and 7-8-9 in the top row, from left to right. So, basically, they evolved from the cash register.

BUT WHEN TOUCH-TONE TELEPHONES WERE INVENTED, WHY DIDN’T THEY SIMPLY REPLICATE THE CALCULATOR KEYPAD ARRANGEMENTS?

Before the touch-tone phone, of course, rotary dials were the rule. The rotary telephone was invention in the early 1900s. Instead of buttons, the numbers on the telephone were holes from 1-9, and then 0. The idea was to stick your finger in the hole and spin it around to dial each number.

In the early 1960s, researchers at Bell Laboratories were preparing to introduce an alternative to the rotary telephone, something they called push-button dialing (which later came to be marketed as “Touch Tone” dialing). But there was one big question in front of them : how to arrange the numbers.

There were two logical models, of course. The existing rotary phone with its circular dial and counterclockwise number arrangement, with the 1 sitting in the upper right, was one. The calculator was the other.

To find the best number arrangement for push-button dialing phones, Bell Labs conducted a study titled “Human Factor Engineering Studies of the Design and Use of Pushbutton Telephone Sets.” This study involved testing several different telephone-keypad layouts to find out which was easiest to master. For this study the researchers simply gave various potential layouts and asked test subjects to fill in what they thought was the best configuration, given a particular layout. It was found that the three-by-three matrix that had 1, 2 and 3 across the top was the easiest for people to use and had the lowest error rate.

On basis of this result, Bell engineers implemented the three-by-three matrix keypad design which people found easy to use and which is still in use today and has been adapted to smartphones as well.