Duo Comptometer

This full-keyboard non-printing adding machine has a black metal case with six columns of black and white, octagonal keys, colored according to the place value of the digits entered. Complementary digits are indicated on the keys. Keys representing even digits are flat, those for odd digits are indented. In back of the keyboard is a movable carriage that contains a counter register and a result register above it. Numbers in the counter register can have up to seven digits. Those in the result register 13 digits.
To the left of the number keys are two white keys, one for the key drive and one for the crank drive. To the right of the number keys is a white key that, when pushed, releases the keys. On the right side of the machine is a crank that may be rotated to enter numbers into the register when the “crank drive” key is pushed down. The machine is designed to combine key-driven addition and crank-driven multiplication. It is the first model of a “Duo” Comptometer, and comes from the collection of models at Felt & Tarrant Manufacturing Company. There is no provision for subtraction.
A patent for the invention was filed July 31, 1923 and granted just over nine years later on August 2, 1932. It is patent 1,869,872. A metal tag stored with the object is marked: 134.
Reference: Felt & Tarrant, Accession Journal 1991.3107.06.
Currently not on view
Object Name
adding machine
date made
Felt & Tarrant Manufacturing Company
Physical Description
wood (overall material)
steel (overall material)
plastic (overall material)
overall: 16.4 cm x 35.6 cm x 34.5 cm; 6 15/32 in x 14 1/32 in x 13 19/32 in
place made
United States: Illinois, Chicago
ID Number
catalog number
accession number
Science & Mathematics
Adding Machines
See more items in
Medicine and Science: Mathematics
Adding Machines
Data Source
National Museum of American History, Kenneth E. Behring Center
Credit Line
Gift of Victor Comptometer Corporation
Additional Media

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