Why 1-2-3 is on bottom row in calculator keypad but on top row in phone keypad?

It was in the mid-90s, during my schooling, when I first came across a telephone in my friend’s house which had a numerical keypad. It looked revolutionary because until then the only phones I had seen were the ones which had rotary dial which was tedious to operate & required patience, while this phone with numerical keypad looked like it was straight out of a science fiction movie.
Since I was pretty much familiar with pocket calculators, even to the extent of keying numbers quickly without looking at them, I immediately tried my hands on this “new-age” telephone but started fumbling right from the word go, as my fingers were acting clueless. My familiarity with calculator keypad numbering layout hardly mattered when I tried to use the telephone keypad, because it had a different numbering layout. In fact, it was somewhat opposite. While the calculator keypad started from 1-2-3 at the lower row, the telephone keypad started from 1-2-3 at the top row. (The same convention was carried on by the telecom industry even for mobile phones)
Anyway, I was too young to think about all these back then, and simply got used to the telephone keypad layout over the years. Maybe the education system in which I grew up was such that one had to simply accept things as they were without questioning, and therefore this question never popped up into my mind. But recently, when I was using the calculator after a long time, I began to wonder. Why on earth would our engineers try to create different standards for calculators & telephones? Was it intentional or just a honest mistake? Could it be due to ego-war between different companies or standardization bodies?

While trying to find out more on this topic, I came across some really interesting facts which might give a very convincing answer to this question, which I think might have haunted many people (especially engineers) or if it had never occurred to them before, then the curiosity might have got triggered after reading the title of this post.

As most of us would already be aware, it was the calculator which came much before telephones. It was mainly used by scientists & engineers, and in many use-cases, they had to deal with large numbers which involved lots of trailing zeroes as well. Since the calculators back then were mechanical, with each digit requiring its own set of internal gears & levers, the developers had no choice but to have multiple columns of keys (usually 8 columns), with each column having 9 keys corresponding to the 9 digits i.e 1 to 9.
Each column represented the number (key) which was pressed. There was no key to represent zero because it was implicit that if the user had not pressed any of the buttons in that column, then it meant the digit represented by that column was zero)

The following picture of such a mechanical calculator would give an idea of how the keys were arranged on such calculators.
As you can see, the lowest row was for the digit 1, the next row above it for 2 and so on, all the way up to 9 on the topmost row. It made logical sense as well because 1 being of the lowest value, was placed at the bottom and 9 carrying highest value was on top. (No button pressed meant it was zero)

The following video gives a demonstration of the operation of such mechanical calculators.

In the mid-20th century, thanks to the advent of technologies like transistors, developers were able to get rid of all mechanical parts, thanks to electronic circuits, they were able to squeeze the whole thing into a tiny device & thanks to electronic displays, they were able to get rid of redundant keys and thereby retain only 10 keys for 10 digits, while using the LED/LCD to display the number being keyed. Since the mechanical calculators had 0 at the bottom and 9 on top, while developing the electronic calculator, developers tried to retain the same convention so that engineers & scientists migrating to these new calculators would not feel awkward.
Ok, it all sounds convincing till here. But now comes the big question. When telecom companies developed phones, why didn’t they simply replicate the calculator keypad layout?

Before going into that, we must first know that the phones which were standardized by Bell Telephone Company & had proliferated throughout America right from the late 19th century had rotary dial, which was basically mechanical design with moving parts.
With the advent of transistors & circuit design, engineers at the Bell Telephone Company (The Bell System) were planning to develop the new-gen phones in 1960s, by replacing the rotary dial with numerical keypad. Since it was an all-new design, engineers in the Bell team could not come to a consensus on what the keypad layout should be. While some engineers were of the opinion that it should be a 5×2 matrix (5 rows, 2 columns), some thought 3×3 matrix would be fine, while few others thought just replicating the calculator layout would be good enough. To resolve this, the engineering team hit upon the idea of conducting experiments with several kinds of keypad layouts and invited hundreds of people to use them & provide their feedback.


The experiment results were published in their tech journal, an excerpt of which is as follows.
Journal in PDF format:

The result of the experiment was loud & clear. People were more comfortable with a keypad layout which had 1-2-3 on top. And it actually made sense, because for a common man who typically reads from top to bottom & from left to right, having 1 on top, with numbers reading from left to right (1-2-3) appeared conventional. Probably, if the Bell team had chosen a sample size consisting of majority of scientists & accountants (who were familiar with calculators), the results would have probably been different, with the majority preferring calculator layout itself to be replicated on telephone as well. But since Bell knew that it was actually catering to a mass-market with common man being the focus, their sample size for the experiment reflected the typical society.

With these experiment results, Bell engineers were not confused anymore, and quickly implemented the design which people preferred, thereby resulting in the keypad layout which is still in use today and has been adapted to cellphones as well, but with a contrasting difference over calculator keypad layout.

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