Have you ever taken a moment to notice your phone uses a number pad inverted to what your computer uses? Have you ever wondered why that happened? On a phone, the number 1 is in the top left, on a keyboard or calculator it's on the bottom left. What could the reason be?
In the early days (1640s-1670s), you had the mechanical "adding machine." They originally had a layout that would not resemble the modern number keypad we know. As we entered into the 20th century, we see the start of the layout we're more familiar with. The design itself was used for cash registers and modern calculators. It was a common layout operators, bookkeepers, and accountants got used to.
Telephones came out after adding machines. In the 1960s, researched were testing different keypad layouts for touch-tone phones. They did not use the same design as a calculator despite it already being established. Studies showed that humans would make fewer mistakes with the layout having number 1 start in the top left.
Each technology had developed separately, meaning it was not actually an intentional inversion. Each layout was optimized for different users and different tasks.
When it comes to computer keyboards, the calculator layout won. Users for computers would likely include accountants and other individuals who were likely already trained on calculators and adding machines, so it made more sense to keep that layout. Not all computers actually included a full number pad originally, though. The IBM Model M released with the calculator-style number pad that helped influence the PC industry to include number pads.
