The Slide Rule
An English Mathematician William Outraged combined the principles of the logarithm Napier's bones to construct the Slide Rule in 1620 A.D. It consists tow scales , one moving over the other . the rules are marked off in such a manner that the distance on the scales is proportional to the algorithm of the numbers. by Sliding one scale over the other one can easily multiply and divide. Engineers and mathematicians extensively used slide rules until the electronic calculation replace them.