"Jubilee Magnum" Circular Slide Rule

Fowlers & Co. (Calculators) Ltd. "Jubilee Magnum" extra long scale circular slide rule, c. 1960, with case and instruction booklet.

The Fowler Calculator is a type of circular slide rule, a sort of mechanical calculating device, popular in the time before electronic calculators were developed.

Slide rules have a number of different moveable scales on them. By moving the scales on the slide rule, counting the number moved, and comparing the results between them, it is possible to do a range of calculations quite quickly, particularly multiplications, divisions, and conversions between different units. Many slide rules are shaped like straight rulers, but this one is pocket-watch shaped, with the scales adjusted by twisting the knobs on the edge.

It was made by Fowler & Co, a Manchester based company, originally established as the Scientific Publishing Company in 1898 by William Henry Fowler. The firm began offering pocket-watch calculators in 1898 and manufactured devices of this type for several decades, with William Fowler and his son Harold patenting several improvements. The firm offered a whole range of calculators, some intended for general use and others manufactured for the calculations common in specific industries.

This particular Fowler "Jubilee Magnum” extra long scale calculator was a design first issued in 1948, the name Jubilee celebrated the 50th anniversary of the firm’s founding in 1898. It was intended to do a range of calculations and is larger than other types of Fowler calculators, allowing it to be read with more accuracy. The long scale makes it easier to do larger calculations.