Excise Officer's slide rule, 1759-1769.

This 12 inch long Excise Officer's slide rule is made of boxwood, and has four sliders, under one of which is inscribed; 'Edwd Roberts Maker in Dove - Court Old Jewry, London'. Slide rules were little known or used outside this country until the beginning of the 19th century. In Britain, however, highly sophisticated slide rules for excise duty were in fairly common use by 1700. Ales and wines were stored in many different casks, so that lengthy calculations were needed to estimate the contents of a partially full cask.