Monroe Model G Calculating Machine

This manually operated, non-printing modified step drum calculating machine has a steel case with plastic keys and wooden handles on the cranks. In the eight columns of keys, the key stems increase in length from front to back. On the right side is a red key for clearing the entire keyboard. Between the rows of keys are metal strips, painted black on one side and white on the other. They turn to serve as decimal markers. Two silver-colored knobs have arrows on them. The one on the right is used for automatic keyboard release in continuous addition. The one on the left is the register key for the item counter.
In back of the keyboard is a carriage with 16 total register dials and eight revolution register dials behind the total dials. The dials of the revolution register are numbered around the edge from 9 to 0 white and from 1 to 9 in red. A metal operating handle with a wooden knob is on the right side. Another handle on the right side of the carriage zeros the total register or the revolution register, depending on the direction in which it is turned. A knob on the right side of the carriage is used to lift it. A crank at the front of the machine is rotated to move the carriage. The machine has four rubber feet.
A mark on the front of the machine reads: MONROE (/) REGISTERED TRADE MARK (/) HIGH SPEED-ADDING-CALCULATOR. A mark on the back of the machine reads: MONROE (/) REGISTERED TRADE MARK (/) CALCULATING MACHINE COMPANY (/) New York, U.S.A. Another mark on the back reads: G22939.
According to McCarthy, Monroe introduced the Model G calculating machine in 1919, using serial numbers above 20,000. Records of the U.S. Patent and Trademark Office indicate that the trademark Monroe was registered in 1920. In 1921 Monroe replaced the Model G and other earlier models with its Model K, hence the date assigned.
The donor of the machine reported that he purchased it used at a flea market or tag sale.
E. Martin, The Calculating Machines (Die Rechenmaschinen), trans. P.A. Kidwell and M.R. Williams, Cambridge: MIT Press, 1992, p. 265.
J. H. McCarthy, The American Digest of Business Machines, Chicago: American Exchange Service, 1924, pp. 80–81, 551.
U.S. Patent and Trademark Office, Trademark Registration 129029, Serial #71117235.
Currently not on view
Object Name
calculating machine
date made
Monroe Calculating Machine Company
Physical Description
steel (overall material)
wood (overall material)
plastic (overall material)
overall: 17 cm x 43 cm x 33 cm; 6 11/16 in x 16 15/16 in x 13 in
place made
United States: New York, New York
ID Number
catalog number
maker number
nonaccession number
Science & Mathematics
Calculating Machines
See more items in
Medicine and Science: Mathematics
Calculating Machines
Data Source
National Museum of American History, Kenneth E. Behring Center
Credit Line
Gift of Burton J. Udelson

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