c1920 Cased Fowler’s Long Scale Circular Calculator

A fine condition example of a Cased British Fowler's Long Scale Circular Calculator (Type 2MG2 according to R. Blankenhorn & R. de Cesaris' Catalogue).

It is a pocket, circular slide rule, calculator in fitted clam-shell metal case. The circular slide rule effectively compresses a long straight slide rule in a compact manageable round one. The calculator is a large pocket watch size, with 2 adjustment knobs and scaled calculation faces, front and back. It is marked: FOWLER’S LONG SCALE CALCULATOR – PATENT – FOWLER & Co. MANCHESTER. The case and calculator body is made of stainless steel. The inside of the case is lined in red baize, with a copper circular plaque with the company details. Condition is good, but with a little bit of wear. The owner’s name: P.M.C. Lacey has been lightly engraved on the outside of the case.

William Henry Fowler (1853–1932) and his son, Harold Fowler, took out several British patents for improvements to circular calculators between 1910 and 1924. The first Fowler calculator with two knobs on the rim was patented in 1914. In 1927, Fowler & Co. introduced the Magnum Long Scale Calculator, which extended the scale length to 50 inches. Thus, this example is dated between 1914 and 1927.

Fowler is a well-known English name in circular slide rules/calculators. The company made a variety of different models and size calculators including many circular versions like this one. Some were designed for architects, or engineers, and others were made for the textile trades. Larger ones are referred to as Magnums, but this model is referred to as the pocket size calculator.

Size face: 63 mm (2 4/8 inches)
Size case: 7 x 7.5 x 1 cm (2 ¾ x 3 x 3/8 inches)
Weight: 157 g