William Oughtred  (1574-1660) was one of the world's great mathematicians.  He attended Eton School and King's College, receiving his M.A. in 1600.  In 1603 he was ordained as an Episcopal minister.  In the 17th century, becoming a clergyman was a common and well respected career option for a well educated man. Like many others of his day, Oughtred was likely not a formally trained mathematician, rather he was largely self-taught.  He reputedly had a burning curiosity for mathematics and along with Harriot, he devised a standardized notation for algebra, some of which remains in use today.

Oughtred's passion for mathematics was so great that he maintained a free school for young men interested in the science.

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  Oughtred published his renowned work Circles of Proportion and the Horizontal Instrument  in 1632.