Otis King's Pocket Calculator Model L Cylindrical Slide Rule

This six-inch cylindrical slide rule consists of a chromium-plated holder, a metal cylinder that slides into the holder, and a black metal tube that fits around and slides up and down on the cylinder. The rule is ten inches long when extended. Two short white lines on the tube and a black mark on the chrome cap at the end of the cylinder serve as the indicator. A paper spiral logarithmic scale is attached to the top half of the holder. A second, linear and logarithmic, paper scale is attached to the cylinder. The logarithmic scales are used to multiply and divide, and the linear scale is used to find logarithms.

At the top of the cylinder is printed: PATENT No 183723. At the bottom of the cylinder is printed: OTIS KING'S POCKET CALCULATOR; SCALE No 430. The top of the scale on the holder is printed: SCALE No 429; COPYRIGHT. The bottom is printed: OTIS KING'S PATENT No 183723. The end of the holder is machine engraved: MADE IN (/) Y5466 (/) ENGLAND.

The instrument arrived in a mailing tube with return address: CALCULATOR COMPANY (/) POST OFFICE BOX 593 (/) LAKEWOOD, CALIFORNIA 90714.

Otis Carter Formby King invented this form of slide rule in 1921, and Carbic Limited of London, England, manufactured it until 1972. The Calculator Company served as Carbic's distributor in the United States. The 5-digit ZIP code on the mailing tube indicates this example was made after 1963. The serial number, Y5466, suggests a date around 1965–1969.

See also 1987.0788.01 and 1981.0922.09. The slide rule was received with a trifold instruction sheet, 1989.3049.03, and an advertising pamphlet, 1989.3049.04.

References: Dieter von Jezierski, Slide Rules: A Journey Through Three Centuries, trans. Rodger Shepherd (Mendham, N.J.: Astragal Press, 2000), 44; Richard F. Lyon, "Dating of the Otis King: An Alternative Theory Developed Through Use of the Internet," Journal of the Oughtred Society 7, no. 1 (1998): 33–38; Dick Lyon, "Otis King's Patent Calculator," http://www.svpal.org/~dickel/OK/OtisKing.html.

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