Description

Otis King Spiral Slide Rule, Model K. Fitted cardboard box, instruction leaflet and a laminated card insert showing the decimal parts of £1 (Lsd) and the decimal equivalents of parts of an inch (from 1/64 to 63/64). The slide rule cost £4 2s 6d to purchase (£4 12½p).

It is a cylindrical slide rule with helical scales with an effective scale length of 66 inches which improves the accuracy of the calculations significantly. The instruction leaflet states that the Model K can be used for “all calculations involving multiplication, division and proportion, including costs, percentages and foreign exchange problems”.

It is designed as a pocket calculator with telescopic scales where the upper scale slides into the wider lower scale when not in use. The leaflet observes that there “can be few industries and professions in which the Otis King would not be found useful” including “Civil Engineering Contractors“.

A video showing how to use the slide rule is available to view here.