Monroe Model 8N-213 Calculating Machine

This fully automatic, non-printing electric modified stepped drum calculating machine has a gray and black steel frame and ten columns of gray and white oblong plastic keys. At the bottom of each column is a clearance key. Between the columns of keys and under the keyboard are metal rods that turn to serve as decimal markers. An automatic keyboard clear switch is in the front. To the right of the number keys are subtraction and addition bars, two carriage shift keys, and a green key. Below these are three levers, one to set repeated entries, one for multiplication, and one for non-entry. Below these are three red keys relating to entering the dividend, a gray keyboard clear key, and a lock lever. Beneath the number keys are five keys relating to multiplication and division. A DIVD ALIGN key is left of these.
In back of the keyboard is a carriage with ten dials to show a number set up for multiplication, 21 dials to show the result, and a row containing ten white dials on the left and then 11 black dials. The white dials are revolution register dials that show multipliers in black or quotients in red. These do not have a carry. The black dials also register the multiplier in multiplication and the quotient in division and have a carry. Above the black dials is a row plastic buttons, eight red and one yellow. The red buttons are tab stops for the carriage, and the yellow button releases the red ones. Sliding decimal markers are provided. A gray-green electric cord plugs into the back of the machine.
A mark on the carriage reads: MONROE. The same mark is on the back of the machine, with the Monroe logo trademarked in 1956. A mark on both right and left sides reads: MONROmatic. A paper sticker glued to the bottom of the machine reads: MONROE (/) CALCULATING MACHINE (/) COMPANY, INC. (/) ORANGE, N.J. U.S.A.. It also is marked with patent numbers that range from 2,250,403 to 2,732,129. The second patent date is from 1953. A metal tag attached to the bottom of the machine reads: MODEL 8N-213 (/) SERIAL J903574. There is no mention of Litton Industries, which acquired Monroe Calculating Machine Company in 1958.
Compare to MA*335425 and 1980.0255.01.
Currently not on view
Object Name
calculating machine
date made
ca 1960
Monroe Calculating Machine Company, Inc.
Physical Description
rubber (overall material)
plastic (overall material)
steel (overall material)
overall: 20 cm x 37 cm x 34.5 cm; 7 7/8 in x 14 9/16 in x 13 19/32 in
place made
United States: New Jersey, Orange
ID Number
catalog number
maker number
nonaccession number
See more items in
Medicine and Science: Mathematics
Science & Mathematics
Calculating Machines
Data Source
National Museum of American History, Kenneth E. Behring Center


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