A few comments about Monroe calculators

by Nicholas Bodley


The author worked for a competitor to Monroe, so this is rather spotty knowledge. Monroe Calculating Machine Company (?) was based, I believe, in Orange, N. J., or some other northern community in that state. It dates back perhaps to the early 1920s, possibly before. Its first models were probably driven by a handcrank on the right side of the "wedge" I have described for the electrically-driven machines. (Their basic design was essentially the same.)

Their first models might not have had the explicit "wedge and carriage" design I have described; late 19th-century and early 20th-century calculators had outer shapes much more distinctive and more closely related to their internal mechanisms, and the first Monroes might have looked similar.

An earlier Monroe had an external drive motor, and was physically rather large; it took up as much desk space as a large typewriter. I owned one, for a while; it was lost in a burglary. Like all Monroes, the main driveshaft turned clockwise (looking at the right side of the machine) to add, and counterclockwise to subtract. This machine required manual shifting and watching the dials to do multiplication and division. It had a removable cover with a knob that allowed you to insert a handcrank (after unplugging the drive motor, I dare say!)

Later Monroes were "miniature" versions of this larger, older basic design, and had internal drive motors. These calculators were light in weight and quite compact, as small as reasonable; their internal parts were quite possibly simply scaled-down versions of the earlier larger parts, with minimal detail changes. Monroes of the later era were relatively sophisticated compared to typical Fridens (although only Fridens did square root, I'm fairly sure). However, they weren't as rugged as Fridens. My recollection is that different models offered quite a variety of levels of automation; some didn't multiply automatically, I believe.

Multiplying on the machines with automatic multiplication (which must have been the majority of those sold) used the main keyboard to enter both operands; I do not know anything about the mechanism that stored the multiplier.

Most Monroes were, I'm fairly sure, either 10-digit or possibly 8-digit machines, with all digits of a maximum product displayed.

To my knowledge, Monroe did not develop its own electronic calculator; I might have forgotten! Perhaps I simply didn't become aware of it.

Probably the pinnacle of mechanical calculator design was the Monroe PC-1421. This was a remarkable machine, with modular construction that made maintenance much easier; it used quite-small molded plastic parts, which meant minimal inertia (a significant problem in mechanical calculators). It was a printer, with completely automatic decimal points; it could accept a 14-digit number via a 10-key serial-entry keyboard, and could print 21-place results. Some day, I hope to see its insides!

Copyright @1997 Nicholas Bodley

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