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Otis King's Pocket Calculator Model L Cylindrical Slide Rule

Otis King's Pocket Calculator Model L Cylindrical Slide Rule

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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 and equivalent to a linear slide rule 66 feet in length. 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.
The end of the cylinder is engraved: MADE IN (/) ENGLAND. 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: T/0503. Engraved by hand (and upside-down to the serial number) is: C73.
The instrument is stored in a rectangular black cardboard box. A label on one end reads: Otis King's (/) Calculator (/) Model "L" (/) No. T0503. The slide rule arrived with instructions, 1987.0788.06, and an advertising flyer, 1987.0788.07. See also 1989.3049.02 and 1981.0922.09.
Otis Carter Formby King (b. 1876) of Coventry, England, received a British patent (183,723) for this instrument on August 31, 1922, and in 1923 he received patents 207,762 and 207,856 for improvements to the slide rule. From London, King filed a U.S. patent application, which he assigned to Carbic Limited, the London manufacturer of the slide rule, when that patent was granted in 1927. With co-inventor Bruce Hamer Leeson, King received U.S. Patent 1,820,354 for an "electrical remote control system" on August 25, 1931.
The serial number indicates that this example of Otis King's calculator was manufactured around 1960 to 1962. Howard Irving Chapelle (1901–1975), a naval architect, maritime historian, and curator of what was then the National Museum of History and Technology, donated it to the Smithsonian around 1969 to 1970.
References: Peter M. Hopp, Slide Rules: Their History, Models, and Makers (Mendham, N.J.: Astragal Press, 1999), 274, 281; Otis Carter Formby King, "Calculating Apparatus," (U.S. Patent 1,645,009 issued October 11, 1927); 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.
Currently not on view
Object Name
slide rule
date made
Carbic Limited
place made
United Kingdom: England, London
Physical Description
chromium (overall material)
paper (part material)
overall: 17 cm x 4 cm x 3.7 cm; 6 11/16 in x 1 9/16 in x 1 15/32 in
ID Number
catalog number
accession number
Credit Line
Gift of Howard I. Chappelle
Rule, Calculating
See more items in
Medicine and Science: Mathematics
Science & Mathematics
Slide Rules
Data Source
National Museum of American History
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