Monroe Model KA Calculating Machine

This full-keyboard, electric, non-printing modified stepped drum calculating machine has a steel frame painted black, with rounded corners. The metal plate under the keyboard is painted green. The six columns of plastic keys are colored black or white according to the place value of the digit represented. A red clearance key is at the bottom of each column. Rods between the rows of keys serve as decimal markers. They are unpainted on one side and painted the same green as the plate under the keyboard on the other.
A column to the right of the number keys has three keys. One clears the entire keyboard. The other two are set to determine whether or not the keyboard clears after each calculation. Above these are plastic bars which may be depressed for electric addition or subtraction. The machine also operates using a removable crank that fits on the right side and rotates clockwise for addition and counterclockwise for subtraction.
In back of the keyboard is a carriage that has a row of 12 numeral dials for recording results and a row of six numeral dials behind these, which serve as a revolution register. The revolution register has no carry. Two thin metal rods between the windows for these registers carry decimal markers. The carriage shift lever is at the front of the machine. To the right of the result register is a knob for lifting the carriage. On the right side of the carriage is the zeroing crank for dials on it. The machine has four rubber feet. The motor is attached to the left side of the machine and has an on-off switch. It has a fraying electrical cord attached. The on-off switch for the bell is on the back left of the keyboard.
A mark on the center back of the machine reads: MONROE (/) Calculating Machine Company (/) New York, U.S.A. A mark on the left bottom edge of the carriage and on the right side of the machine under the carriage gives the serial number A20317. The machine is from after 1924 and before 1939. In the later years, it was known as the KA-120.
J. H. McCarthy, The Business Machines and Equipment Digest, 1928, pp. 9-29 to 9-33.
Currently not on view
Object Name
calculating machine
date made
ca 1930
Monroe Calculating Machine Company
Physical Description
steel (overall material)
rubber (overall material)
aluminum (overall material)
plastic (overall material)
wood (overall material)
cloth (overall material)
overall: 19.8 cm x 47 cm x 37 cm; 7 25/32 in x 18 1/2 in x 14 9/16 in
place made
United States: New York, New York
ID Number
catalog number
maker number
accession number
See more items in
Medicine and Science: Mathematics
Science & Mathematics
Calculating Machines
Data Source
National Museum of American History, Kenneth E. Behring Center
Credit Line
Gift of Victor Comptometer Corporation

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