If users are unable to print item labels, the item barcode may be invalid. A barcode is invalid when its check digit is incorrect. A check digit is a number appended to the data contained in a barcode. A Check digit is used to assure accuracy; to "check" for errors. It typically consists of a single digit computed from the other digits in the data.
To check if a barcode is valid, consider the following:
- For 12 digit bar codes (UPCA types of bar codes)
- Sample bar code is 134688257347
- Add the digits in the odd-numbered positions (first, third, fifth, etc.) together and multiply the total by three.
■ 1+4+8+2+7+4=26
- Multiply what you got on step 1 by 3
■ 26 * 3 = 78
- Add the digits in the even-numbered positions (second, fourth, sixth, etc.).
■ 3+6+8+5+3=25
- Add the two results together.
■ 78 + 25 = 103
- Now what single digit number makes the total a multiple of 10? That's the check digit.
■ 103, to make it a multiple of 10, it needs 7
■ 7 is the check digit that must be the last digit of the bar code
- For 13 digit bar codes (EAN type)
- Sample bar code 1346882573478
- Starting from the second position, add all the digits in an even-numbered positions (second, fourth, sixth) together.
■ 3+6+8+5+3+7=32
- Multiply what you got on step 1 by 3
■ 32*3=96
- Add all the digits in an the odd-numbered positions together
■ 1+4+8+2+7+4=26
- Add the two results together
■ 96+26=122
■ 122, to make it a multiple of 10, it needs 8
■ 8 is the check digit that must be the last digit of the bar code