EASY-TRACK™ AUDIT SYSTEM
American Games bingo paper is protected by a fool-proof audit system that lets you track the bingo sheets and booklets that have been played.
In the example shown below, the indicator number "3H-1504" indicates that the book is the 1504 of the set of 3000 3H books in the set. (9000 faces to the set divided by 3 faces per card yields 3000 books.)

From this, you can tell that 1503 books have been sold and 1497 books remain in the set.