history of Napier's Bones

Napier's Bones

John Napier, a Scottish mathematicianm created logarithm tables to facilitate calculations. He also created a device using rods, also called Napier's Bones to perform arthimetic calculations.
 These rods were widely used by accountants and bookkeepers. Several people used the concept to logarthms to develop the slide rule. With a modren sliderules you could onlyperform the arithmetic operations, but also calculate squares, square roots, logsmsinem cosine and tangent. 
The slide rule was used till middle 70's