touchback - (American football) a play in which the opposing team has kicked the football into your end zone.
From Wikipedia, the free encyclopedia. A check digit is a form of redundancy check used for error detection on identification numbers, such as bank account numbers, which are used in an application where they will at least sometimes be input manually. It is analogous to a binary parity bit used to check for errors in computer-generated data.
Check numbers tend to run in the thousands, 4 or 5 digits; routing numbers are 9 digits; and account numbers are typically 9 or 10 digits. The logic behind these numbers is, of course, based on powers of ten.