How to Validate GTIN Barcode Check Digits Using GS1 Mod-10

The GS1 Mod-10 algorithm calculates the check digit for GTIN barcodes like EAN-13. It multiplies every second digit from the right by 3, sums all digits, and computes the check digit as the amount needed to reach the next multiple of 10. A Python implementation demonstrates the process, which applies to UPC-A, EAN-13, GTIN-8, and GTIN-14.