The 123 on the bottom makes some sense for calculators because calculator keypads, unlike telephone keypads, are often used to enter data, physical constants, and mathematical constants.<p>Those quite often follow Benford's Law [1]. That means if you are using scientific notation, where numbers consist of one digit to the left of the decimal point, the decimal point, and then a fractional part, then an exponent for the power of 10 the number is to be multiplied by, then you are much more likely to be entering a small digit before the decimal point than a large digit.<p>123, therefore, arguably belongs near the decimal point on the keypad on calculators.<p>[1] <a href="https://en.wikipedia.org/wiki/Benford%27s_law" rel="nofollow">https://en.wikipedia.org/wiki/Benford%27s_law</a>
The article mentions the 1960 Bell System user study of different keypad layouts. I can't speak to the other layouts, but I think in hindsight it's clear why the "touch tone" layout (with 123 at the top) won over the the "calculator" layout (with 789 at the top).<p>Everyone or nearly everyone in the user study was surely a <i>telephone user</i>. At the time, that meant being accustomed to the rotary dial layout, where the order of the digits is 1234567890. 0 is the last digit, after 9.<p>Both the calculator and touch tone layouts had 0 at the bottom. So the calculator layout has 0 next to 123. The touch tone layout has 0 next to 789 (and following the 9), just like a rotary dial.<p>This must have accounted for some of the preference between these two layouts.
The numeric keypad on computers has stayed remarkably consistent given how adept manufacturers are at moving the other keys around the keyboard. It is not a given that Page Up/Down, cursor keys, the delete key and others will be where you expect them to be by convention, these keys can be moved around for 'designer reasons' even on keyboards from the same manufacturer (yes, you, Logitech).<p>I have yet to see the numeric keypad on the left for left handed users that type in lots of numbers, e.g accountants, data entry clerks etc. We also never had desktop computers integrated into landline phones with a 'phone lock' button to switch over to 'dial someone' mode. At all times the numeric keypad has opted to follow convention as defined by the original IBM PC circa 1981.
This reminds me of the two opposing conventions for drawing memory maps --- do you put "lower" (numerically lesser) addresses at the bottom and increase to "higher" addresses at the top, or start with 0 at the top and "increase" downwards? Just like with the Endianness Wars, it seems that multiple conventions often prevail when there isn't a clear and obvious advantage of one.
One of the articles cited is available for free: <<a href="https://archive.org/details/bstj39-4-995>" rel="nofollow">https://archive.org/details/bstj39-4-995></a>. I find it interesting to note that the engineers also made variable force profile pushbuttons to test different springinesses as well.
> In 1902, the Dalton went on to become one of the most popular 10-key adding machines of the time, rendering multi-column calculators obsolete.<p>Multi-column calculators survived much longer, being king of the hill for high-accuracy multiplication and division. I had a job using one until the end of 1969.
On rotary phones, zero was usually at the bottom of the rotar, just after the after nine. When touch tone phones came out, I suspect many people preferred the zero at the bottom of the keypad since it was near the nine and better aligned with their existing muscle memory