International Standard Music Number
The International Standard Music Number (ISMN) was designed in cooperation
with the ISBN community.
It is pretty similar to the ISBN code, but
there are some differences, especially in the calculation of the
check-digit.
The first part (ISBN-country code) is changed to the single letter M,
there is no separate country code, the remaining eight digits are
publisher and publication number as with the ISBN.
The check-digit is calculated by multiplying the last digit of the
true (8-digit) code by 3, the last but one by 1, etc. alternating
between 3 and 1, until you reach the letter M.
This one you should multiply by 3 (it has the weight 3).
The check digit is the number that need to be added to reach a
multiple of 10.
When encoded in an EAN-13 barcode the code is preceded by the digits 979,
the letter M is replaced by the digit 0.
Due to the way the check-digit is calculated, the ISMN check-digit is
identical to the EAN check-digit.