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Question Mark TOWER Mystery 3  Why are the buttons on calculators and telephones lined up in a different order?
Calculator buttons are numbered 0 to 9, bottom to top. Telephone buttons are numbered 1 to 9, top to bottom, with 0 at the end. They both use the number 0 through 9, but why do you think they are lined up in opposite directions?
Calculator buttons are numbered 0 to 9, bottom to top, because people thought it would be better to have the number 0, which is used the most often in calculations, closest to the user. But calculator buttons were not always lined up in the same way. The 14-A, which was Casio’s first calculator, had keys lined up just like today’s calculators, but the world’s first desktop calculator, built by a British company six years later, was a “full-key” model, which meant it had a row of 10 keys for each digit. Full-key calculators continued to be built for a while, but they finally disappeared because more people thought calculators with buttons numbered 0 to 9, bottom to top, and usable for any digit, were easier to use. These days, the International Standards Organization (ISO) has made a standard or rule for how number buttons should be lined up on computers and calculators.
a Calculator and a Phone

The way buttons are lined up on telephones is defined by the International Telecommunications Union, Telecommunications Sector (ITU-T) as 1 to 9, top to bottom, with 0 at the end, because that is the most natural. When calculators first appeared, telephones used a dial instead of buttons.

So, as you can see, calculators and telephones belong to different standardization groups, and the different way their keys are lined up is the result of those groups choosing which way was easiest to use.

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