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" closed length is the equivalent of a 66" 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. The cylindrical design was very sturdy and stable but expensive for example in 1960 the Otis-King sold for approximately 5 Pounds in England, while a good quality wood/celluloid rule cost only approximately 30 Shillings.

Stainless steel casing circular tube construction in two parts, with knurled flat-domed top which pulls up revealing slide rule. The top part of casing is free when slide rule is extended. Numbers printed on paper, stuck on metal slide rule works on same principle as the Fuller spinal slide rule

This has Otis King cylindrical slide rule has Made In England on one end and the reference T/1253 on the other end. It has Otis King's Patent Number of 18723 with a Scale number of 423 and the name: Otis King's Pocket Calculator

It is believed to be the K model but if any one can enlighten us further please email collection@computinghistory.org.uk.

Our unit was very kindly donated by Julian Bryant.

Manufacturer:
Date: 1960

This exhibit has a reference ID of CH21941. Please quote this reference ID in any communication with the Centre for Computing History.

Click on the Image(s) For Detail