Monroe Model L160-X Calculating Machine

This lightweight modified stepped drum full-keyboard non-printing calculating machine is manually operated. It has a gray steel case and gray and white plastic keys, colored to distinguish digits of differing place value. The eight columns of keys each include nine digit keys and one zeroing key. The zeroing key is the opposite color from the rest of the keys in the column. Between the columns of keys, and under the case, are metal rods visible through windows in the case. These serve as decimal markers. To the right of the number keys are two orange buttons, one of which is marked R (for use in repeated addition or subtraction), and an orange 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 dials of the revolution register are numbered around the edge from 9 to 0 white and from 1 to 9 in red. A crank for clearing the carriage is on its right side. The carriage shift crank is at the front. Two rubber feet are at the front and two metal standing pieces extend from the back at the bottom, holding the machine at an angle.
This model of the Monroe normally came with a carrying case, but this does not survive.
Compare MA*336523 (1978.0402.01).
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
Object Name
calculating machine
date made
Monroe Calculating Machine Company
Physical Description
rubber (overall material)
plastic (overall material)
steel (overall material)
overall: 15 cm x 29.4 cm x 23.7 cm; 5 29/32 in x 11 9/16 in x 9 11/32 in
ID Number
catalog number
maker number
L160-X 628561
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


"Yes, these machines can do long division and long multiplicationThe top row of digits does NOT carry - instead they go from red 9 red 8 ... black 0 black 1 .. black 9The handle at the r end of the carriage clears the top row of digits when rotated one way, and the lower row when rotated the otherTo do long division (eg: 123 / 45), clear the lower row, put 123 into the keypad, move the carriage so the 123 will go into the high end, and rotate the body handle clockwise once to put 123 into the middle row.This will also put a 1 into the top row. Clear this by rotating the carriage handle. Now put 45 into the keypad and depress the R (Repeat) button - middle of the three buttons in the lower R side of the keyboard. This stops the machine from clearing the keypad after a single subtract.Rotate the body handle counterclockwise to do a subtract. 1 is SUBTRACTED from the top row showing a RED 1, and the 45 is subtracted from the 123 leaving 78 and a red 2. Rotate again leaving 33. If you rotate again a bell will ring and lots of 9's will appear in the high end of the middle row as well as the 3 appearing in the top row. Rotate clockwise to add the 45 back in and get back to a red 2. Now turn the handle at the front of the keyboard anticlockwise to move the carriage one position, and repeat as aboveBasically you are doing good ole' fashion long division but using repeated subtraction to discover the right digit for each column of the resultThe electric machines with the auto divide do exactly this. They have a trigger attached to the 9's appearing in the high end of the middle row that cause them to switch to doing an add. The same trigger sees the 9 going away again and does the carriage movement before switching back to subtracting. A second trigger detects when the carriage can't go any further.Multiplication is a simpler version of these steps - basically clear the rows, put one of the two factors into the keyboard, depress the Repeat button, and use repeated addition and carriage shifting to construct the other factor in the top row! You can do this in any order, since at any time - provided you have no badly overflowed a counter=dial in the top row - the middle row will be the top row times the keypad number!Hope this helps/Bevin"
"could this calculator perform multiplication and division? I know more advanced models included the division lever to the upper left of the keyboard area but I'm wondering if the process of division could have been performed manually, especially since the display carriage can be moved to left justified."
"This calculating machine did not perform automatic multiplication or division. The operations were carried out one decimal place at a time, shifting the carriage between subtotals."

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