16.1 Check Digits Universal Product Code - UPC - Video

Key Idea The Universal Product Code (UPC) is a twelve-digit code, a1a2a3a4a5a6a7a8a9a10a11a12, including a check digit at the end. By multiplying each digit by its weight, (alternately 1 for even positions, 3 for odd positions and then adding), the sum must be a number ending in 0.