Napier's bones, 1671-1700.

John Napier (1550-1617), discoverer of logarithms, created the popular calculating tool known as Napier's rods or bones. Napier's rods reduced muliplication to a sequence of simple additions; division and square roots could also be achieved. This instrument consists of a wooden box containing ten rotating cylinders each of which bears the numbers '0 times' to '9 times'.