Monroe Calculating Machine (Model D?)

This is an early model of the full-keyboard, modified stepped drum, manually operated non-printing calculating machine manufactured by the Monroe Calculating Machine Company on patents of Frank S. Baldwin.
The machine has a steel frame painted black. The eight columns of plastic keys are colored black or white according to the place value of the digit represented. The key stems are banked, standing up further toward the back of the machine. At the front of the keyboard is a row of red keys each of which clears the column above it. On the right side, in this row, is a red key for clearing the entire keyboard. There are no strips between columns of keys. 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 black 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 9 to 1 in red. The metal operating handle with a wooden knob painted brown 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. There is no knob to lift the carriage. An all-metal crank at the front of the machine is rotated to move the carriage. The carriage has sliding decimal markers for both registers.
The machine is marked at the center of the back edge, underneath the carriage: 20. A mark on the front reads: MONROE (/) Calculating Machine Company (/) New York. There is no mention of a trademark. A sticker on the back reads: PATENTED JUNE 16, 1908 (/) OTHER U.S. AND FOREIGN PATENTS (/) PENDING.
Compare to MA*317389. Both machines have the same number of keys, the same number of entries in the revolution counter and result registers, and the same mark on the sticker on the back. The mark on MA*317389 mentions a trademark. The color-coding of the keys, the color of the machine handles and shift lever, and the mechanism for the carriage shift differ between the machines. Object MA*317389 has rotating rods that serve as decimal dividers on the keyboard, and a considerably larger serial number, which begins with a D. Hence that machine is given a slightly later date.
E. Martin, The Calculating Machines (Die Rechenmaschinen), trans. P. A. Kidwell and M. R. Williams, Cambridge: MIT Press, 1992, p. 265.
Currently not on view
Object Name
calculating machine
date made
Monroe Calculating Machine Company
Physical Description
steel (overall material)
wood (overall material)
aluminum (overall material)
plastic (overall material)
overall: 15.9 cm x 42 cm x 31.5 cm; 6 1/4 in x 16 17/32 in x 12 13/32 in
place made
United States: New York, New York
ID Number
catalog number
maker number
none found
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


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