the wheels would be used to zero them. Subtraction was possible by adding complementary numbers; keys would also carry a smaller, complementary digit to help the user form complementary numbers. Division was also possible by putting the dividend to the left end and performing repeated subtractions by using the complementary method.

Some adding machines were electromechanical - an old-style mechanism, but driven by electric power.

Some "ten-key" machines had input of numbers as on a modern

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