Citation :
UPC
The final digit of a Universal Product Code is a check digit computed as follows:[1]
1. Add the digits (up to but not including the check digit) in the odd-numbered positions (first, third, fifth, etc.) together and multiply by three.
2. Add the digits (up to but not including the check digit) in the even-numbered positions (second, fourth, sixth, etc.) to the result.
3. Take the remainder of the result divided by 10 (modulo operation) and subtract this from 10 to derive the check digit.
4. If the last digit of the result in step 2 is 0, then the check digit is 0.
For instance, the UPC-A barcode for a box of tissues is "036000241457". The last digit is the check digit "7", and if the other numbers are correct then the check digit calculation must produce 7.
1. We add the odd number digits: 0+6+0+2+1+5 = 14
2. Multiply the result by 3: 14 × 3 = 42
3. We add the even number digits: 3+0+0+4+4 = 11
4. We add the two results together: 42 + 11 = 53
5. To calculate the check digit, take the remainder of (53 / 10), which is also known as (53 modulo 10), and subtract from 10. Therefore, the check digit value is 7.
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