Perfection Self-Adding Ruler

The wooden ruler also serves as a stylus-operated non-printing adding machine. It has a plastic inset along the middle, with a perforated paper strip that moves below the plastic. The numbers from 1 to 45 are marked along one edge of the plastic and from 46 to 90 along the other. A small dial and a window are at one end. Instructions are given on a plastic insert on the reverse of the rule. The number in the window indicates units and tens, while those around the dial denote hundreds. Only one of the hundreds digits (3) is marked. There is no stylus. One edge of the ruler is beveled and has a brass insert. This edge is marked off with a scale 15 inches long, divided to 1/16 inches.
The device is marked: PERFECTION (/) SELF-ADDING RULER (/) PAT. JAN. 8th 1895. No place of manufacture is indicated. The inventor, Robert E. McClelland, lived in Williamsville, Illinois. Later versions of the rule indicate that it was made in New York.
Robert E. McClelland, “Computing Machine,” U.S. Patent 532241, January 8, 1895.
Currently not on view
date made
McClelland, Robert E.
place patented
United States: Illinois, Williamsville
Physical Description
paper (overall material)
plastic (overall material)
wood (overall material)
brass (overall material)
overall: .8 cm x 38 cm x 4 cm; 5/16 in x 14 31/32 in x 1 9/16 in
ID Number
accession number
catalog number
Credit Line
Gift of L. Leland Locke
See more items in
Medicine and Science: Mathematics
Science & Mathematics
Adding Machines
Data Source
National Museum of American History


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