[UI] Phone Keypads and Calculator Keypads are arranged in different way

Some daily object may make you surprised that they are design for different usage but looks similar. The phone keypads and calculator keypads are one of the example.

Now, do not find any tips, do you know which keypad is for calculating? and which is for dialing?

I believe this may takes you time to think but you will get right answer anyway.

As you could see the number arrangement is reversed. But you never feel odd when you want to phone or do calculating. Everything is smooth and reasonable. Even they looks the same but the story of these two interface is totally different. Below are some information I found and it could simply group into two section: user behavior and invention history.

(Image from vcalc.net)

User Behavior

Some saying on the internet mentioned that calculators are often use on the desk and 0 and 1 is the mostly used numbers under binary system. So the smaller numbers are putting at the bottom.

Some of the phones are installed on the wall, such as those in the telephone booth. The reversed number arrangement is easier for dialing.

(Image from homewetbar.com)


The key pads on the first calculators actually resembled old cash registers. And soon David Sundstrand, invented the first 10-key calculator in his brand — , with the left row of keys numbering 9 on top down to 0 on the bottom and later morphing into the more traditional keypad we see today. The keypad design quickly become standard and the electronic calculator producer following the same way.

Sundstrand 10 key keypad closeup circa 1914
(Image from retrocalculators.com)

Yet the design of phone keypad has a more interesting story. On the rotary telephone dial, the numbers are 1 on top and 9 on bottom, 0 follows 9 at the end. So it has same number arrangement on the phone keypad.

(Image from therotaryshoppe)

While not only the reason above, but a study done by Bell Labs called “Human Factor Engineering Studies of the Design and Use of Push button Telephone Sets” has focus on finding out the the optimal configuration. Various potential layout was given and ask the test subjects which is the easiest one to master. The result is the three by three matrix which number 1 to 3 across the top was the easiest for people to use.

(Image from todayifoundout.com)

If you try to aware on the daily objects, you may find out there are reasons or stories behind them.

Images and reference from:
Keyboard Trivia
Why are the numbers on a calculator and a phone reversed?
Sundstrand Adding Machine — Underwood Sundstrand

Originally published at iscmlam.wordpress.com on July 16, 2017.