Napier's Rods, 1671-1700.

John Napier (1550-1617), discoverer of logarithms, created the popular though comparatively trivial invention of the calculation device 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'. Logarithms made the manipulation of large calculations simpler by adding or subtracting the index of two numbers and looking up the result in tables.