Monroe  Electromechanical Calculators
Monroe MA7
Monroe.jpg (10518 bytes)
Monroe CSA-10
Mmatic.jpg (9203 bytes)
"The first picture is a Monroe model MA7, serial MA7-213-258460. The same model is illustrated in an advertisement dated 1937 on Erez Kaplan's web pages. About 15 years ago I completely disassembled and cleaned this machine, and prepared about 20 pages of notes and sketches of its workings. I reckoned that I knew and understood the function of every part by the time it was back together.

The seond picture is a Monroe-Matic, model CSA-10, serial 651918. This is quite a compact machine - the keyboard is only 5 inches square, and the body (excluding carriage) is just on 9 inches wide. The "-matic" presumably comes from its capability for automatic multiplication (since both machines do
automatic division).

The multiplication process is rather more straightforward (for the operator, at least) than on other brands. On the Marchant Figurematic there is a separate column of keys to enter the multiplier, and the machine adds and shifts as each digit is entered. On some Fridens there is a separate 10-key keypad to enter the multiplier. On the Monroe-matic the main keyboard is used to enter both numbers, one after the other (just like on a modern calculator), and then the machine carries out all the adds and shifts automatically and displays the answer:

- set the first number on the keyboard, press "Enter X". This stores the number internally and displays it in the small register below the accumulator.

- set the second number (all the digits, not just one at a time), press "Clear/Mult". The machine then automatically performs all the adds and shifts, clears the multiplier register, and returns the carriage to the leftmost position.

Both these machines are in good working order.

John Wolf

Source: John Wolf

X-Number World of Calculators