EAN-13 Check Digit Calculation
Symbol above depicts EAN-13 bar code. Last 13-th digit in this barcode is the check digit (the "5").
As you see in EAN-13 the check digit, a single checksum digit. The check digit is computed modulo 10, where the weights in the checksum calculation alternate 1 and 3. In particular, since the weights are relatively prime to 10 the EAN system will detect all single digit errors. But since the difference of consecutive weights is even, the EAN system does not detect all adjacent transposition errors.
How-to calculate EAN-13 Check Digit
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To calculate EAN-13 check digit you can use interactive tool o this web-site: Check Digit Calculator
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Make Sure you enter all thirteen digits (you can use the 0 for the last one that you do not know - the tool will correct you if necessary).
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Example of EAN-13 that is correct: Correct Check Digit
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Example of EAN-13 that is incorrect: Incorrect Check Digit