The check digit is calculated in the same way as an ISBN-13, and in turn, an
EAN-13. Specifically, each digit of the ISMN is multiplied by a weight, alternating 1 and 3 from left to right. These weighted digits are added together. The check digit is the integer between 0 and 9 that makes the sum a multiple of 10. The check digit for a pre-2008 code, M-xxxx-xxxx-c is computed in the same manner as the EAN check digit for the 13-digit code obtained by replacing M with 9790. In other words, the old and new codes differ only by the replacement of M with 9790, with no change in the check digit. This differs from, for example, the ISBN to EAN mapping where the check digit must be recalculated.
Examples For instance, for the item with ISMN beginning 979-0-060-11561: : 1×9 + 3×7 + 1×9 + 3×0 + 1×0 + 3×6 + 1×0 + 3×1 + 1×1 + 3×5 + 1×6 + 3×1 : = 9 + 21 + 9 + 0 + 0 + 18 + 0 + 3 + 1 + 15 + 6 + 3 : = 85 As 85 mod 10 = 5, the check digit is 10 − 5 = 5 and the full number is 979-0-060-11561-5. For another example,
Robert Fripp's collection of
Guitar Craft scores has the ISMN 979-0-9016791-7-7. Given first 12 digits 979-0-9016791-7, the ISMN algorithm evaluates : 1×9 + 3×7 + 1×9 + 3×0 + 1×9 + 3×0 + 1×1 + 3×1 + 1×6 + 3×7 + 1×9 + 3×1 : = 9 + 21 + 9 + 0 + 9 + 0 + 1 + 3 + 6 + 21 + 9 + 3 : = 123 which implies that the check digit is indeed 7 (because 123+7=130=13×10). ==See also==