Circular slide rules

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Fowlers Long Scale

Fowler's double sided Long Scale Calculator, complete with velvet lined nickel plated case. Known also as a 'vest pocket' model, these double sided calculators were regarded as comprehensive and accurate. It measures 2.5 inches in diameter. Full instructions with worked examples can be found on

D Scale length: 980 mm. Significant digits: 3.7 to 4.

Copyright 2012, Dave Hoyer.