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.
The Cutter number for a book usually consists of the first letter of the author's last name and a series of numbers. This series of numbers comes from a table that is designed to help maintain an alphabetical arrangement of names.
When the library has several works by the same author, a "work mark" is used to distinguish the various works of a single author. The work mark is a lower case letter that is usually the first letter of the title of the book. Let’s use the Harry Potter books as an example:
Remember that the Cutter number is a decimal not a whole number and is also read digit by digit.