2. How the
International Standard Music Number (ISMN)
is constructed

An International Standard Music Number (ISMN) consists of the letter "M" followed by nine digits. Whenever it is printed or written, the number is preceded by the letters "ISMN."

Note: In countries where the Latin alphabet is not used, an abbreviation in the local script may be used in addition to the Latin letters "ISMN."

2.1. Elements

The ISMN is divided into four elements, two of which are of variable length. When the ISMN is printed, each element is separated by a hyphen or space.
The four elements are as follows:

2.1.1. Distinguishing element

The letter "M" distinguishes the ISMN from the ISBN.

2.1.2. Publisher identifier

This element identifies a particular publisher.

The publisher identifier designates the publisher of a given music publication. Publishers with a large output are assigned short publisher identifiers; publishers with a small output are assigned longer publisher identifiers. (For the distribution of publisher identifiers according to their variable length see Chapter 2.2.).

2.1.3. Item identifier

This element identifies an edition of a work and the various items within it, e.g. full score, miniature score, set of wind parts, oboe part, etc. An item, in the terms of the Standard, is one separately saleable or available or obtainable constituent part of a music publication.

The item identifier is assigned to a particular item by the publishers from within the range of numbers assigned to them. The length of the item identifier depends upon the length of the publisher identifier.

Item identifiers are normally assigned by the publishers themselves (but see also Chapter 5 on non-participating publishers). Publishers who assign their own item identifiers may use them to identify items in the publishing house throughout the planning stages, items they only publish as hire materials, etc.

2.1.4. Check character

This is a single digit at the end of the ISMN that provides an automatic verification of the correctness of the ISMN. It is computer-calculated.

The check character is calculated on a modulus 10 with alternating weights of 3 and 1 assigned from left to right beginning with the letter "M" prefix. The letter "M" counts as 3.

This means that each of the first nine characters of the ISMN--i.e., excluding the check digit itself--is multiplied by an alternating sequence of the numbers 3 and 1 from left to right. The sum of the products thus obtained, plus the check digit, must be divisible by 10 without a remainder.

   Example:

As 70 can be divided by 10 without remainder, M-3452-4680-5 is a valid International Standard Music Number.

 2.2. The number of digits in each element and how to recognize them in an ISMN

The number of digits in the identifying elements 2 and 3 is variable, though the total number of digits contained in these elements is always 8. These eight digits together with the check digit and the preceding letter "M" bring the total number of digits in an ISMN to ten.

Publishers with an expected large output will get numbers of 3 or 4 digits. Publishers with a small output will get numbers of 5, 6 or 7 digits.

For ease of reading, the four elements of the ISMN are divided by spaces or hyphens. These spaces or hyphens, however, are not retained in the computer which recognizes the internal structure of the ISMN by matching the first three or more numbers with the ranges of publisher identifiers.

The following table shows one possible arrangement of publisher identifiers:

Looking at a published item M 299102349, it will be seen that while there cannot be a publisher with the identifier 299, there can be a publisher with the identifier 2991. Even with the proper spaces between three elements of this number omitted, a glance at the identifier ranges will show that the publisher identifier element of this number must be 2991.