William Oughtred (1574–1660)
Letter to Elias Allen
England, 20 August 1638
MS Add. 9597/13/5/215

This letter from the mathematician William Oughtred to the instrument maker Elias Allen accompanies a narrow two-foot-long print that is the only evidence we have of the very first slide-rule. The print was made directly from the slide-rule itself (long since lost), rather than from a normal printing plate. It dates from 1638, more than a decade after the principle of this kind of calculating device had been developed by Oughtred. The reason for the delay is not known; in this letter to Allen, Oughtred says that he ‘would gladly see’ the slide-rule, ‘wch yet I never have done’. From this we can be certain that the print is a record of the first example of an instrument that was in use right up to the invention of modern electronic calculators in the 1960s.