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Why do some ISBNs end in an “X”?

April 26, 2017ISBNs

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Why do some ISBNs end in an “X”?

1 Answer

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10 Posted

In the case of the check digit, the last digit of the ISBN, the upper case X can appear. The method of determining the check digit for the ISBN is the modulus 11 with the weighting factors 10 to 1. The Roman numeral X is used in lieu of 10 where ten would occur as a check digit.