An International Standard Book Number is assigned to each edition and variation of a book.
=== ISBN-13 check digit calculation ===Appendix 1 of the International ISBN Agency's official user manual:33 describes how the 13-digit ISBN check digit is calculated
For example, the check digit for an ISBN-10 of 0-306-40615-? is calculated as follows:Adding 2 to 130 gives a multiple of 11 (because 132 = 1211)  this is the only number between 0 and 10 which does so

