Wilhelm Schickard

Schickard's calculating machine, about 1623 Wilhelm Schickard, a university professor, minister, astronomer and engraver, built two calculators around 1623 and described one in a letter to his friend Johannes Kepler. His design combined a set of Napier's rods for multiplication and division with a toothed-wheel adder for addition and subtraction, which makes it the earliest known mechanical four-function calculator. Neither machine survives: Kepler's was destroyed by fire and the other is lost. The design was known only from sketches and letters that stayed lost until 1935. It earns its place as the first attempt to make gears do the carrying a human clerk would otherwise do in their head.