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Understanding Call Numbers




Reading

To be able to efficiently read Library of Congress (LC) call numbers is quite a skill. This tutorial was created to help library users uncover the mysteries of call number reading. Let's start with a sample call number:

QE534.2.B64

Call numbers can begin with one, two, or three letters.

  • The first letter of a call number represents one of the 21 major divisions of the LC System. In the example, the subject "Q" is Science.
  • The second letter "E" represents a subdivision of the sciences, Geology. All books in the QE's are primarily about Geology.
    • Books in categories E, United States History, and F, Local U.S. History and American History, do not have a second letter (exception: in Canada, FC is used for Canadian history).
    • Books about Law, K's, can have three letters, such as KFH, Law of Hawaii. Some areas of history (D) also have three-letter call numbers.
  • Most other subject areas will have call numbers beginning with one or two letters.
    • For most of the subject areas, the single letter represents books of a general nature for that subject area (i.e. Q - General Science or D - General World History).

Numbers after letters.

  • The first set of numbers in a call number help to define a book's subject.
  • "534.2" in the example teaches us more about the book's subject. The range QE 500-625 are books about "Dyamic and Structural Geology."
  • Books with call numbers QE534.2 are specifically "Earthquakes, Seismology - General Works - 1970 to Present"
  • One of the most frequently used number in call numbers is "1" which is often used for general periodicals in a given subject area.
    • For example, Q1.S3 is the call number for the journal Science.
  • Journals are also given call numbers based on the specific subject.
    • For example, QE531.E32 is the call number for the journal Earthquake Spectra as QE531 is the class number for periodicals about "Earthquakes, Seismology"

Cutter Number

  • The cutter number is a coded representation of the author or organization's name or the title of the work (also known as the "Main Entry" in library-lingo).
  • Charles Ammi Cutter first developed cutter numbers using a two-number table.
    • A three-number table was developed in 1969.
  • In our above example, QE534.2.B64, the B64 is taken from the two-number table and represents the author's last name, Bruce A. Bolt.
    • The book is Earthquakes.
  • Some books have two Cutters, the first one is usually a further breakdown of the subject matter.
    • For example, QA 76.76 H94 M88 is a book located in the Mathematics section of the Q's.
      • QA 76 is about Computer Science.
      • The ".76" indicates Special Topics in Automation.
      • "H94" tells us that this is a book about HTML.
      • "M88" represents the last name of the first author listed's last name, Musciano.
      • The book is HTML: The Definitive Guide

Shelving and Locating

Items are shelved by call numbers - in both alphabetical and numerical order. The letters at the beginning of the call number are alphabetical. The numbers immediately following are in basic numerical order, i.e. 5 then 6, 50 is after 49 and before 51, and 100 is after 99. Thus,

QD 1
A3
QD 2
A 31
QD 3
Z 4
QD 29
C 3
QD 30
A 2

The cutter numbers (A3, A31, Z4, C3, and A2 in the above example) are sorted first by the letter and then by the number as a decimal. For QD 1 A5 think of it as being QD 1 A 0.5, for QD 1 A332 read QD 1 A 0.332. Therefore,

QD 1
A3
QD 1
A 31
QD 1
A 311
QD 1
A 4
QD 1
A 41
QD 1
A 415
QD 1
A 42

Dates, volume and issue numbers, copy numbers, and other annotations are like an additional cutter number but are shelved by basic alphabetization (numbers alone come before letters):

Q 10
C 3


Q 10
C 3
1933

Q 10
C 3
1990

Q 10
C 3
1996
copy 1
Q 10
C 3
1996
copy 2
QD 1
A 5
Vol. 1

QD 1
A 5
Vol.2

QD 1
A 5
Vol. 2
Plates
QD 1
A 5
Vol. 2
Supplement


To the Library of Congress Classification index

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