1948 Fowler Long Scale Jubilee Magnum extra long scale calculator Fowler’s “Jubilee Magnum” Circular Slide Rule Dimensions: 4–3/4” diameter, 7/16” thick. Weight: 10 oz. Manufactured: Fowler’s (Calculators) Limited, Sale, England, (Estab. 1898)
Fowler & Co. of Manchester built a range of circular “pocket calculators” over a period of almost 70 years from 1898. They were produced in single or double-sided models, generally with plated metal bodies and glass covers. The scales and cursors were rotated independently by external buttons or milled nuts. The “Jubilee Magnum extra long scale calculator” was introduced in 1948 to mark the company’s 50th anniversary. It is typical of a class of slide rules which operate with two cursors on a single logarithmic scale.
The distance between the cursors is set to the first factor, and the cursors are moved together (or the scales are moved beneath them) to add or subtract the set distance from the second factor. The three outermost scales on this rule are a single-turn logarithmic scale about 13 inches long, an inverse log scale, and a linear scale. Various constants and conversion factors are marked around the outer edge of the dial. The separate “extra long” scale makes ten turns around the dial for a total length of over 70 inches. The scale turns are circular rather than spiral, with steps outwards at the index line (see detail). The instructions recommend a check calculation to ensure that the result is being read on the correct turn of the scale. http://home.vicnet.net.au/~wolff/calculators/sliderules/sliderules.htm
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