Locke Adder

The first American-made adder to enjoy modest commercial success was developed by Clarence E. Locke (1865-1945). A native of Edgerton, Wisconsin, he graduated from Cornell College in Mt. Vernon, Iowa, in 1892. Locke worked for a time as a civil engineer in Minnesota, and then joined his father operating a lumberyard in Kensett, Iowa.
This version of the device has a metal base with grooves for nine sliding metal rods that move crosswise. Each rod represents a digit of a number being added. Protruding knobs on the rods represent different numerals. The rods are held in place by bronze-colored metal covers that extend over the right and left thirds of the instrument. When the device is in zero position, all the rods are in their rightmost position.
Numbers are entered by sliding rods to the left, and the result appears in numbers immediately to the left of the cover on the right. The rods are color-coded to distinguish units of money. They lock when depressed, so that they will not slide if the instrument is tilted. The locking mechanism, the color-coded rods, and the oval shape of the knobs on the rods are all improvements featured in Locke’s second calculating machine patent, taken out in 1905. There is no carry mechanism. The base of it is covered with green cloth.
The instrument is marked on the right cover: C.E. LOCKE (/) MFG. Co. It is also marked: KENSETT, IOWA. [/] U.S.A. It is marked on the left cover: THE (/) LOCKE (/) ADDER. It is also marked: PATENTED DEC. 24. 1901 (/) JAN. 3 1905. The instrument fits in a cardboard case covered with black cloth.
According to the donor, the example of the Locke adder was given to him by the retiring operator of a country milk receiving station for a dairy. The operator used it to determine the total number of pounds of milk received each day at the station.
References: C. E. Locke, “Calculating Machine,” U.S. Patent 689680, December 24, 1901.
C. E. Locke, “Calculating Machine,” U.S. Patent 779088, January 3, 1905.
Robert Otnes, “Sliding Bar Calculators,” ETCetera #11 (June 1990): pp. 6-8.
P. Kidwell, “Adders made and Used in the United States,” Rittenhouse, 8, (1994): pp. 78-96.
Accession file, for advertising brochure and history of the instrument.
Currently not on view
date made
C. E. Locke Manufacturing Company
place made
United States: Iowa, Kensett
Physical Description
paper (overall material)
metal (overall material)
cloth (overall material)
overall: 2 cm x 29.5 cm x 12.3 cm; 25/32 in x 11 5/8 in x 4 27/32 in
ID Number
catalog number
accession number
Credit Line
Gift of Earl L. Hemenway
See more items in
Medicine and Science: Mathematics
Science & Mathematics
Data Source
National Museum of American History, Kenneth E. Behring Center


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