Monroe Model F Calculating Machine

This full-keyboard, non-printing manually operated modified step drum calculating 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 entered. 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 clearance keys for the individual columns above. On the right side is a red key for clearing the entire keyboard. Between the rows of keys are metal strips, painted black on one side and white on the other. They turn to serve as decimal markers. The 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 white revolution register dials behind the total dials. The revolution register dials are numbered around the edge from 0 to 9 in white and then from 9 to 1 in red. Metal strips on the carriage carry sliding decimal markers for the registers. Ther metal operating handle with a wooden knob 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. A shaped metal piece on the left side of the carriage is used to lift it. A crank at the front of the machine rotates to move the carriage.

A mark on the front of the machine reads: MONROE (/) Calculating Machine Company (/) New York. A mark in the middle of the back reads: F6981. A tag on the back of the machine reads: PATENTED JUNE 16, 1908 (/) OTHER U.S. AND FOREIGN PATENTS (/) PENDING. A mark on the plastic cover reads: MONROE.

According to McCarthy, the Monroe Model F was introduced in 1917, with serial numbers above 6,000. In 1920, Monroe was granted a trademark for the name Monroe, and used the term “registered trademark” on its machines. Hence the approximate date assigned to this machine.

References:

E. Martin, The Calculating Machines (Die Rechenmaschinen), trans. P. A. Kidwell and M. R. Williams, Cambridge: MIT Press, 1992, p. 265.

J. H. McCarthy, The American Digest of Business Machines, Chicago: American Exchange Service, 1924, pp. 80–81, 551.

U.S. Patent and Trademark Office, Trademark Registration 129029, Serial # 71117235.

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