Here's the Wikipedia entry about ITF, the barcode in use. https://en.wikipedia.org/wiki/Interleaved_2_of_5 Note that the reader expects the last digit to be the [checksum](https://en.wikipedia.org/wiki/Universal_Product_Code#Check_digit_calculation) (which is optional from the definition point of view and isn't used by the scanners), which typically makes our numbers have an odd number of digits. To make the number even again, the padding "0" is added in front.