I'd argue that the most common calculators are the four-function calculators (plus GT, MR etc.) used by sellers worldwide in the non-Western world that don't wa

I'd argue that the most common calculators are the four-function calculators (plus GT, MR etc.) used by sellers worldwide in the non-Western world that don't want to use full-function POS systems and still use paper ledgers – the ones with solar cells and battery lifetimes in the order of months. While they used to have special-purpose controllers, sadly, they seem to be shoving Android in them now... perhaps for a good upgrade path, though. [1] [1] https://www.youtube.com/watch?v=ui2UVUXiIzY https://www.youtube.com/watch?v=ui2UVUXiIzY