There are two main types of cylindrical slide rules: those with helical scales such as the Fuller, the Otis King and the Bygrave slide rule, and those with bars, such as the Thacher and some Loga models. In either case, the advantage is a much longer scale, and hence potentially higher accuracy, than a straight or circular rule. The 6 inch closed length is the equivalent of a 66 inch slide rule.

The Otis-King rule uses concentric telescoping metal cylinders with a continuous long spiral logarithmic scale. Calculations are done by sliding and rotating the cylinders relative to each other. The purpose of using a cylinder design slide rule is to increase the length of the scales, thereby improving the accuracy, relative to the linear type.

This Otis King cylindrical slide rule has 'Made In England' on one end and the reference X5452 on the other end. It has Otis King's Patent Number of 183723 with a Scale number of 414, 423 and the name: Otis King's Pocket Calculator.

Other models had different scales: this is the K model and is complete with box, manual, and decimal/imperial conversion card.

Kindly donated by Harry Feather.

Manufacturer: Otis King
Date: 1960

This exhibit has a reference ID of CH39875. Please quote this reference ID in any communication with the Centre for Computing History.

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