In 1966, the National Bingo Association (NBA) adopted a rule specifying that all bingo cards must include a free space at the bottom. As playing cards became more common, however, manufacturers began using cardstock for bingo cards, which eliminated the need for players to use paper. The practice of including a free space on bingo cards originated in 19th century England, where players would use small pieces of paper to keep track of which numbers had been called. The purpose of this space is two-fold: first, it allows the caller to keep track of which numbers have been called, and second, it helps to ensure that all players have a fair chance of winning.
Typically feature a free space at the bottom, which is where the bingo caller marks off the numbers as they are called.