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Advertising Archive - Monroe 820A

Monroe 820A Flyer

For the longest time, the Monroe 820/820A was a bit of an enigma, simply due to the fact that no examples of the machine had been found. However, recently, the museum has acquired both a Monroe 820 and 820A. These machines are quite unique due to the fact that it appears that it was designed and manufactured by Litton/Monroe. This is unusual in that other than Monroe's first two electronic calculators, Monroe moved to OEM relationships with other calculator companies such as Olympia, Canon and Compucorp, and selling the machines under the Monroe brand, with subtle feature and cabinet design changes to provide brand differentiation. The 820/820A looks similar to a Canon designs of the period, but there are no records of Canon ever making a CRT-display calculator. Like Canon, there is also no record of Compucorp building a CRT-based calculator, and, on top of that, Compucorp made higher-end scientific calculators, not desktop four-bangers. Monroe did OEM some later calculators from Singer(Friden), but the 820/820A machine is unlike any of Friden's 116x-series CRT-display calculators, which used RPN logic, and were much larger than the 820. Based on observation of the insides of both the 820 and 820A machines, they indeed appear to have been developed and manufactured by Monroe rather than being a rebadged machine made by another calculator manufacturer.

Along with the machines, (neither of which is operational), the museum has acquired a number of pieces of marketing literature, including this "INSTRUCTIONS" pamphlet, that document the machine. This pamphlet was useful in understanding the operation of the calculator. The pamphlet was published in 1970 and documents the 820A machine. The 820 was introduced in August of 1969. It appears that the 820A variant was introduced sometime in early 1970. The Monroe 820 in the museum was manufactured sometime in the late 1969 time period based on date codes on parts inside the machine. The museum's 820A was built in early 1970 by this same metric.

The 820 is a basic four-function electronic desktop calculator. It operates with fixed or floating decimal with settings for 2, 3, or 4 digits behind the decimal for fixed mode. Numeric entry uses floating decimal, and leading zero suppression is performed to make the display more readable. The 820 does not have the accumulation mode slide switch that the 820A has.

The 820A adds an accumulation mode in which the machine will automatically total sums of products or quotients. This mode is controlled by a slide switch on the keyboard panel.

Overflows cause the display to flash, an audible signal to sound (I'm sure that the audible warning was not popular in office environments), and the numeric and function keys to be electronically locked out. Pressing the [C] key will clear the machine and unlock the overflow condition. Addition and subtraction operate arithmetically, and multiplication and division operate algebraicly, with the [=] key finishing off multiplication and division problems. The "diamond" (subtotal) and [*] (total) keys copy the accumulator register to the entry register, and in the case of the [*] key, the accumulator is then cleared.

The machine is rather unique in that it uses a small CRT display as its display. The display presents two lines of 14 digits. The top line displays the accumulator register (where results of arithmetic operations are placed), and the bottom line is the entry register, where input from the keyboard is entered. Digits are rendered on the CRT display in a seven-segment fashion. The logic of the machine is implemented by small-scale DTL integrated circuits in dual-inline plastic packages, combined with a fairly sizable complement of discrete components that are used in the display generation circuitry.