© David G. Hicks

Slide Rule

William Oughtred

If you were a math or science student born before 1958, you most likely performed math using a slide rule instead of a calculator or computer. By 1974, pocket calculators largely replaced the slide rule.

The slide rule was invented around 1620–1630, shortly after John Napier's publication of the concept of the logarithm. Edmund Gunter of Oxford developed a calculating device with a single logarithmic scale, which with additional measuring tools could be used to multiply and divide.

The first description of this scale was published in Paris in 1624 by Edmund Wingate (c.1593–1656), an English mathematician, in a book entitled L'usage de la reigle de proportion en l'arithmetique & geometrie. The book contains a double scale, one side a logarithmic scale and the other a tabular scale. In 1630, William Oughtred of Cambridge invented a circular slide rule and in 1632 he combined two Gunter rules, held together with the hands, to make a device recognized as the modern slide rule. Like his contemporary at Cambridge, Isaac Newton, Oughtred taught his ideas privately to his students but delayed in publishing them. Like Newton, he became involved in a vitriolic controversy over invention priority with his one-time student Richard Delamain and the prior claims of Wingate. Oughtred's ideas were only made public in publications of his student William Forster in 1632 and 1653.