About Call Numbers:
Library books are organized by their call number, which is composed of two parts: the Dewey Decimal Classification number and the Cutter number.
In large libraries, it is possible that many books will be classified with the same Dewey classification number. The library must give each book a unique number that serves as the address for locating each book on the shelf.
To create this unique number, a Cutter number is added to the classification number.