Check digits

A check digit, also known as a checksum character, is the number located on the far right side of a bar code. The purpose of a check digit is to verify that the information on the bar-code has been entered correctly.

example
step 1: lay out the bar code
1 4 5 6 3  6 7 0 2 2
step 2: times them out in a pattern of 1s and 3s
1 4 5 6 3 6 7 0 2 2
x x x x x x x x x x x 
1 3 1 3 1 3 1 3 1 3
1 12 5 18 3 18 7 0 2 6
step 3: add all of your values up
1+12+5+18+3+18+7+0+2+6= 72
step 4 : take away that number from that number rounded up to the nearest 10
80-72= 8
step 4: this number will be the check digit in your bar code
1 4 5 6 3 6 7 0 2 2 8