A check digit is a digit added to a number (either at the end or the beginning) that validates the authenticity of the number. A simple algorithm is applied to the other digits of the number which yields the check digit. Check Digit Scheme can be used when an end-user has entered in a credit card number and you want to validate it before sending it an authorization.
This self-checking scheme (referred to as the Luhn Mod-10 Method) is an international standard for validating card account numbers (ISO 2894/ANSI 4.13). Such account numbers, which cannot exceed 19 digits including the check digit, are assigned, embossed and encoded to include a single check digit in the rightmost position. The check digit is calculated as follows:
15-Digit Account Number 7951-0287-9015-54?