William Oughtred  (1574-1660) was one of the world's great mathematicians.   A contemporary of Oughtred's, Edmund Gunter, devised a logarithmic rule in 1620, which could be used to multiply and divide using a pair of calipers.  Oughtred was the first to see that a simpler and more sophisticated method of multiplication and division could be achieved by placing two logarithmic rules side by side and using the position of the numbers relative to each other to calculate the desired results.  He also developed the circular slide rule, which operated in the same fashion as a linear slide rule, except that it makes use of an inner and an outer ring