The checksum is a Modulo 10 calculation:
Add the values of the digits in the even-numbered positions: 2, 4, 6, etc.
Multiply this result by 3.
Add the values of the digits in the odd-numbered positions: 1, 3, 5, etc.
Sum the results of steps 2 and 3.
The check character is the smallest number which, when added to the result in step 4, produces a multiple of 10.
Example: Assume the barcode data = 001234567890
>0 + 2 + 4 + 6 + 8 + 0 = 20
>20 * 3 = 60
>0 + 1 + 3 + 5 + 7 + 9 = 25
>60 + 25 = 85
>85 + X = 90 (nearest equal or higher multiple of 10), therefore X = 5 (checksum)
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