Comptometer Model W.M.

This full-keyboard non-printing adding machine is a relatively late example of the products of Felt & Tarrant Manufacturing Company of Chicago. It has a gray-green metal case, a metal mechanism, and plastic keys.
The ten columns of color-coded green and white octagonal plastic keys have nine keys in each column. Complementary digits are indicated and the keys are alternately concave (odd digits) and flat (even digits). The key stems are flat and have no springs around them. The case slopes up toward the back, so that the amount of key stem that protrudes is the same for all digits. A row of subtraction buttons is below the number keys and a row of decimal markers is in front of it. Digits in the running total appear in a set of 11 windows in front of the keys. Digits in the total under columns of white keys are black, while result digits under columns of green keys are red. A red correction key to the right of the keyboard that releases the keyboard after a partial keystroke error has been corrected. A a metal zeroing lever also is right of the keyboard.
The serial number, stamped on the keyboard on the right at the front, is: W.M. (/) 446522. The front and back sides are marked: COMPTOMETER. Several dates are marked on the bottom of the machine with various initials. They include 8/17/45 and12-12-50. A metal plate attached to the bottom of the machine lists 33 patent numbers. Behind the keyboard is the mark: FELT & TARRANT MANUFACTURING CO. CHICAGO, USA.
The model M Comptometer was introduced in October of 1939, starting with serial number 400,001. By March 1947 some 64,500 of these machines had sold. The WM was a “War Model,” adjusted to conserve materials.
This example is from the collection of calculating machines assembled by Myron R. Smith.
Currently not on view
Object Name
adding machine
date made
ca 1945
Felt & Tarrant Manufacturing Company
Physical Description
steel (overall material)
plastic (overall material)
rubber (overall material)
aluminum (overall material)
overall: 15.5 cm x 27.5 cm x 36.7 cm; 6 3/32 in x 10 13/16 in x 14 7/16 in
place made
United States: Illinois, Chicago
ID Number
maker number
W.M. 446522
catalog number
accession number
See more items in
Medicine and Science: Mathematics
Science & Mathematics
Adding Machines
Data Source
National Museum of American History, Kenneth E. Behring Center


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