Monroe Calculating Machine (Model L?)

This small key-set manually operated non-printing modified step drum calculating machine has a steel case painted black with white and gold round color-coded plastic keys. The eight columns of keys have nine digit keys and one zeroing key in each column. The zeroing key is the opposite color from the rest of the keys in the column. Between the columns of keys and under the light green plate are metal rods, visible through windows in the plate, which serve as decimal markers. These rods are painted red on one side and the same green as the plate on the other.
To the right of the number keys are two red buttons, one of which is marked R (for use in repeated addition or subtraction), and a red clearance key. A crank on the right side rotates clockwise for addition and counterclockwise for subtraction.
In back of the keyboard is the carriage, with 16 result dials and eight revolution register dials. The revolution register dials are numbered from 0 to 9 in black and 1 to 9 in red. Between the windows of these registers are two thin metal rods that carry decimal markers. A crank for clearing the carriage is on its right side and another one for shifting the carriage at the front.
The machine has two rubber feet at the front and two collapsible metal standing pieces extending from the back at the bottom, so that it is held at an angle. The standing pieces fit up within the frame of the machine, and the entire device fits in a case covered with black leather. A black cover for the machine fits inside the case.
A mark on the front of the machine and on the cover reads: Monroe. A sticker attached to the right side of the machine reads: COUNTY BUSINESS MACHINES (/) CBM; Phone 235-9034 (/) RICHMOND. The serial number scratched on the underside of the carriage at the left, is 418947.
Compare to 1993.0396.01. Dated from serial number.
This is the “Executive Model” of Monroe’s Model L calculating machine. The “160” signifies the 16-digit result, the X the presence of the case. Manually operated machines were designated simply as “L.” Those operated electrically were “LA.”
National Office Machine Dealer’s Association, Blue Book, May 1975, as compiled by Office Machine Americana, January 2002.
Monroe Calculating Machine Company, “Monroe High Speed Adding-Calculator,” Publication 780-A. This is a notebook with advertising descriptions of several Monroe calculating machines.
Currently not on view
date made
Monroe Calculating Machine Company
Physical Description
rubber (overall material)
wood (overall material)
plastic (overall material)
steel (overall material)
leather (overall material)
overall: 11.7 cm x 32.5 cm x 30.5 cm; 4 19/32 in x 12 25/32 in x 12 in
ID Number
catalog number
accession number
Credit Line
Gift of Norman E. Spiro
See more items in
Medicine and Science: Mathematics
Science & Mathematics
Calculating Machines
Data Source
National Museum of American History


We, at the Camp Pendleton History and Museum Division, have a Monroe Model L Adding-Calculator in our collection. It is in a carrying case with a "How to Operate" pamphlet and another brochure.

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