Hart's Mercantile Computing Machine

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The instrument consists of three concentric brass discs, a brass marker, a steel stop, and a wooden handle (instrument must be removed from box to find handle). Each brass disc has the numbers from 0 to 99 stamped around the edge. The two inner discs both have a circle of 100 holes just outside the numbers. The inner holes are used to add the last two digits of a number by rotation. Any hundreds value in the sum carries to the second set of holes, which are used to add hundreds and thousands places.
The machine is in a cylindrical wooden case with cover.
According to the Kirksville Missouri Democrat for July 26, 1888, by then Hart had sold 3500 of these devices and “he lately ordered one thousand more.”
References: U.S. Patent #199289
P. Kidwell, "Adders Made and Used in the United States," Rittenhouse, 1994, 8:78-96.
Kirksville Missouri Democrat, July 26, 1888.
Currently not on view
Credit Line
Gift of Mrs. Robert T. Kerr
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Medicine and Science: Mathematics
Science & Mathematics
ID Number
accession number
catalog number
Hart, William
Scovill Manufacturing Company
place made
United States: Connecticut, Waterbury
place patented
United States: Missouri, Kirksville
Physical Description
steel (overall material)
brass (overall material)
wood (overall material)
overall: 5.5 cm x 13.5 cm x 13.5 cm; 2 5/32 in x 5 5/16 in x 5 5/16 in
National Museum of American History
Object Name
adder with carry