Pre-Scored Punched Card for Monroe CR-1 Card Reader

This is a larger view of the punched card used for entering programs into Monroe 1600 and 1800-series programmable electronic calcualtors. The card is pre-scored for punching using an IBM Port-O-Punch device that aids in punching out the pre-scored holes and collecting the chad. The holes can also be punched out by hand using a pointed object like a pencil point, but the Port-O-Punch makes the job much easier. The cards encode a nine-bit octal program code, using 3 groups of 3 rows to encode each octal digit of a three digit instruction. The bottom row of punches is a validation row that must be punched in order for a column to be recognized.