Napier's bones, c 1690.
© Science Museum / Science & Society Picture Library
John Napier (1550-1617), discoverer of logarithms, also created this popular calculating tool known as Napier's cylindrical 'rods' or 'bones'. Napier's rods reduced multiplication to a sequence of simple additions and could also be used for division and to calculate square roots. This set is made from boxwood, with a boxwood case.