How to Read Call Numbers

The Library of Congress Classification System

Books and journals are arranged on our shelves according to the Library of Congress (LC) classification system. Using this system, each book or journal is assigned an alphanumeric call number based on its subject focus. This call number uniquely identifies the item and places it on our shelves near other material on the same subject.

Each call number consists of several parts. For example, consider the call number:
TK
7881.6
M29
1993

The FIRST line, TK, defines the class and subclass. These letters specify a broad subject area. Within Class T for technology, TK represents the subclass electrical engineering.

The SECOND line, 7881.6, is the classification number. It should be read as a whole number with a decimal component to determine its location on the shelf. In combination with the class and subclass, the classification number defines the subject matter more finely. In this example, TK7881.6 represents magnetic recording (a subdivision of TK— electrical engineering).

The THIRD line, M29, is called a "Cutter Number." This letter-number combination usually indicates author, but it may also represent other information such as further subject subdivision or geographic area. The Cutter number is always present in a call number and may sometimes be a "double Cutter" (TK7881.6 M29 D45 1992 has a double Cutter). The numeric component of the Cutter number is ALWAYS interpreted as a decimal number when determining shelf location. Therefore, the numeric component of M29 should be read as ".29" (and the call number TK7881.6 M29 1993 should file BEFORE TK7881.6 M4 1993).

The YEAR of publication, 1993, may also be present. Not all call numbers will include the year of publication, but most recent books will. These file in chronological order and often distinguish among varying editions of a text.

Other miscellaneous descriptors may be part of the call number. If present, these will usually differentiate the components of a work that has one title but was published as separate volumes or in parts over time.

In using a call number to locate a book on the shelf, consider each component of the call number in turn before moving on to the next segment.

To find specific subjects, search OskiCat using Keywords as your search type. Then, identify the call numbers for relevant books from your search and browse for other books near these call numbers.

If you have difficulty locating items on the shelves or have other questions about call numbers, please ask at the Reference Desk.