This four-wheeled stylus-operated adding machine has two copper-colored wheels for cents and two silver-colored wheels for dollars. There are numbers on the cover around each wheel. No complementary digits are indicated. Above the wheels are four windows that indicate the total. At the back is a plastic container for the metal stylus. Inside the lid of the case is a so-called magic slate for jotting down and erasing numbers. The adding machine, stylus, and slate fit in an aluminum case. The instrument is marked: Ken + Add MACHINES CO. DULUTH, MINN. U.S.A. PATENT APPLIED FOR.
An account of the Ken + Add appeared in Mathematics Teacher in December 1952, where it was recommended not only as a practical adding machine but as a fascinating toy and an aid to arithmetic teaching. It was advertised in Arithmetic Teacher as late as 1956.
P. A. Kidwell, A. Ackerberg-Hastings, and D. L. Roberts, Tools of American Mathematics Teaching 1800-2000 , Baltimore: Johns Hopkins University Press, 2008, pp. 248-249.
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