Charpentier Calculimetre Multidisc Circular Slide Rule

This brass circular slide rule is the size and shape of a pocket watch. The base is a silver-colored disc surrounding a rotating brass ring. The silver-colored indicator, which moves the brass ring and a forked pointer screwed to the center of the instrument, is attached to a small suspension ring. The indicator extends around the back of the instrument for use in reading the scales inscribed there.

Three scales are on the front: two logarithmic scales on the outermost rings (the equivalent of D and C scales on a linear slide rule) and a two-part scale for square roots around the silver-colored circle at the center (corresponding to the A scale on a linear slide rule). Around the center is engraved: CALCULIMETRE G. CHARPENTIER; BREVETÉ S.G.D.G. The serial number 35 is engraved below "Charpentier." The back of the instrument bears a scale of equal parts, a logarithmic scale, and an innermost scale of equal parts. The indicator arm is engraved: FRANCE.

Around 1882, G. Charpentier patented this design in France (as indicated by the "breveté" mark) and Great Britain. Several French instrument makers manufactured the device. In the United States, the Calculimetre was retailed for $5.00 by Keuffel & Esser from 1895 to 1927 and by Dietzgen from 1904 to 1931. According to the donor, John W. Olson, a Wall Street investment banker and collector of "unusual items" named Edward Hamilton Leslie purchased this slide rule around 1925.

References: Robert K. Otnes, "The Charpentier Calculator," Journal of the Oughtred Society pilot issue, vol. 0, no. 0 (1991): 9–11; Florian Cajori, A History of the Logarithmic Slide Rule and Allied Instruments (New York: Engineering News Publishing Company, 1909), 94; Peter M. Hopp, Slide Rules: Their History, Models, and Makers (Mendham, N.J.: Astragal Press, 1999), 81, 161, 193; Catalogue & Price List of Eugene Dietzgen Co., 7th ed. (Chicago, 1904), 174; Catalogue of Keuffel & Esser Co., 33rd ed. (New York, 1909), 307.

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