Cylindrical slide rule of Otis King's Pocket Calcultor Patent N. 183723 Scale 422-424 from the 1930s, in chromed brass.

Cylindrical slide rule of Otis King's Pocket Calcultor Patent N. 183723 Scale 422-424 from the 1930s, in chromed brass.

Size:  maximum length 23 cm, minimum 14 cm, diameter 3 cm.

In 1630 an English mathematician, the Reverend William Oughtred (1574-1600), manufactured the first slide-rule slide rule. The effectiveness of the slide rule as a tool to quickly perform multiplications and divisions, but also squares, roots and many other operations through the addition or difference on logarithmic scales, was appreciated only from the end of the eighteenth century. Special versions were prepared for particular activities, for example to measure timber, iron bars, barrels, cattle, to calculate taxes on wines and spirits. Rulers for chemical equivalences were also built, to calculate rents, barometric heights, photographic exposure time.

Otis Carter Formby King (1876-1944) was a grocer and engineer in London who invented and produced a helical scale cylindrical ruler.