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Casual Library Assistants Resource Guide: Library of Congress Classification System

How to Read an LC Call Number

Reading call numbers

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 "Dynamic 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, "Bolt."
    • The book is Earthquakes by Bruce A. Bolt
  • 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 represents 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 by Chuck Musciano

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  
A31

  QD 3  
Z4

  QD 29  
C3

  QD 30  
A2

 

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  
A31

  QD 1  
A311

  QD 1  
A4

  QD 1  
A41

  QD 1  
A415

  QD 1  
A42

 

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  
C3
 

  Q 10  
C3
1933

  Q 10  
C3
1990

  Q 10  
C3
1996
 copy 1 

  Q 10  
C3
1996
 copy 2 

  QD 1  
A5
Vol. 1

  QD 1  
A5
Vol. 2

  QD 1  
A5
Vol. 2
Plates

  QD 1  
A5
Vol. 2
 Supplement 

Practice Exercises with Library of Congress Call Numbers

 

This section contains examples of call numbers. Please look carefully at these examples; some of them may require closer inspection than others.

The following example contains three call numbers that are very similar except for one difference.

QC

981.8
.G56
G578

QC

981.8
.G56
G578
2002

QC

981.8
.G56
G578
2006

 

You’ll notice that the only difference in these call numbers is the date. Remember that “nothing comes before something.” That is why QC 981.8 .G56 G578 comes before QC 981.8 .G56 G578 2002, etc.

Is the next example in the correct order?

N

6537
.L522
H454
1988

N

6537
.L54
A2
2000

N

6537
.O39
M48
2001

N

6537
.O39
P48
1991

 

The example is in the correct order. If you thought there was an error, chances are good that your confusion was caused by the Cutter numbers. The Cutter numbers are easy to confuse as being whole numbers. It is also easy to get "tunnel vision" when reading call numbers and neglect the alpha portion of the Cutter numbers. Here is the example again with the potentially confusing Cutter numbers in bold.

 

N

6537
.L522
H454
1988

N

6537
.L54
A2
2000

N

6537
.O39
M48
2001

N

6537
.O39
P48
1991

 

Remember that Cutter numbers are always read as decimals. Which call number below is out of place?

 

M

1010
.M95
B6
1987

M

1010
.M95
B59
1987

M

1010
.M952
B595
1987

M

1010
.M98
B65

 

Did you find the book that is out of place? Look carefully at the bold Cutter numbers below.

 

M

1010
.M95
B6
1987

M

1010
.M95
B59
1987

M

1010
.M952
B595
1987

M

1010
.M98
B65

 

Because we read Cutter numbers as decimals, these two books need to be switched to look like the following:

 

M

1010
.M95
B59
1987

M

1010
.M95
B6
1987

M

1010
.M952
B595
1987

M

1010
.M98
B65

 

Cutter numbers can be very tricky....

It is very important to take your time when shelving and to look carefully at every aspect of a call number.

 

 

Take a look at the following call numbers and decide if they are in the right order. What are the differences between each call number?

PN

197.52
.G59567
B76
1989

PN

197.6
.G59567
B76
1989

PN

197.649
.G59567
B76
1989

PN

197.68
.G59567
B76
1989

 

They are in the correct order. The only difference is in the subject number lines. Now look at the next example. Are the call numbers in the right order? What is the difference between each of the call numbers?

 

Z

1003.3
.E85
S7613
1999
c.1

ZA

1003.3
.E85
S7613
1999
c.1

ZA

1003.3
.E85
S7613
1999
c.3

 

These are also in the correct order. The difference between the first call number and the other two is that the first one contains Z while the other two both contain ZA. The difference between the second and the third call numbers is the copy number. It is important to pay careful attention to the small details. It can be very easy to pass over an incorrectly shelved book when you do not carefully inspect the entire call number.

 

The following example is ordered incorrectly. How should they be ordered?

DA

247.3
.A637
F22
2006

DB

766
.H266
B76

DB

766
.H2556
B76
2003

DB

766
.H2556
B132
2009

DG

247.1
.H502
C821
2000

DC

325.5
.H567
C81
2000

 

The correct order is as follows:

 

DA

247.3
.A637
F22
2006

DB

766
.H2556
B132
2009

DB

766
.H2556
B76
2003

DB

766
.H266
B76

DC

325.5
.H567
C81
2000

DG

247.1
.H502
C821
2000

 

  

Review

  • A final example of correctly ordered call numbers:

K

558
.A23342
M827

1997

K

558
.A23342
M83

2008

K

558
.A2845
B773

1977

K

564
.T3369
C43

2000

K

564
.T575
C4

2000

 

  • Remember that the first numbers in a call number are read as whole numbers, but the Cutter numbers are read as decimals. A book may have two Cutter numbers. If the Cutter numbers become confusing, add zeros to the end of the smaller number to give them both the same amount of digits.
  • Be sure to bring the books to the edge of the shelf when edging.
  • Do not rush when shelving or shelf-reading. It is important that you take your time so that the task is done correctly with as few errors as possible. Remember: a misshelved book is possibly a lost book!

 

 

Library of Congress Classification System

All USask Library locations use the alphanumeric Library of Congress Classification (LCC) System. This system allows us to arrange materials next to each other on the shelves that are about the same or similar subjects. As a Casual Library Assistant 1, part of your responsibility will be to use this system to shelve books and ensure that the shelves are properly ordered. This guide will teach you how to use the LCC system to shelve books, shelf-read, and to perform general stack maintenance.

The LCC system allows books to be arranged by subject into 21 subject classes.  Each book is assigned an alphanumeric call number based on its subject matter. 

For a detailed look at the LCC Outline, click here.

(This guide was adapted from the Library of Congress Classification LibGuide, by Joseph E. Petta, Passaic County Community College Library. It has been edited for content.)