checksum

A checksum is calculated from the data using a known formula that returns a single-digit value and is stored with the data. At any point the checksum can be recalculated to see if the value has changed. The final digit in a universal product code (UPC) is a checksum calculated from the two five-digit parts. The checksum is calculated during scanning, and if the calculated checksum does not match the checksum printed in the bar code, the scan is incorrect. The use of a parity bit is a very simple checksum.