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Monroe 1800-Series Calculator Mark Sense Program Card

Monroe 1800-Series Mark-Sense Program Card, Circa 1974
Used in Monroe CR-2 Mark Sense Card Reader

The CR-2 Mark Sense Card Reader could be connected to any Monroe 1800-series programmable calculator, allowing program information to be leaded from the card into the calculator's memory simply by inserting the card into the CR-2 reader. The CR-2 reader's motor draws the card through the reading station automatically, with the card exiting throug the rear of the reader. The information encoded on the card is transferred into the calculator's memory. A total of 30 program steps can be coded onto one of these cards, one step in each column of the card. The program steps are encoded into 8-bits, in octal (base-8) representation. A filled-in box (using a #2 pencil) represents a binary 1, while leaving a box unfilled represents a binary 0. The bottom-most box in each column allows the instruction encoded in the column to be ignored if the box is filled in, to allow for incorrectly coded columns. The black marks near the bottom of the card are timing marks, read by the photoelectric reading mechanism of the card reade to generate the timing for reading the data from the card. Each card is made of standard punch-card stock, and is printed with a reddish-pink ink, which is invisible to the mark sensors in the reading station of the CR-2.

Thanks for Andrew M. Andrews III for donation of a large number of these cards to the Old Calculator Web Museum