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Research Tutorial

The Call Number System

Books in the Mortensen and Allen libraries are arranged using Library of Congress (LC) call numbers. LC call numbers use a combination of letters and numbers to place a book on the shelf within its subject.

To find books on the shelf using LC call numbers, you must find the first letter(s) which indicate a broad subject. They are arranged alphabetically. So, on the shelf you could see books with call numbers in this order:

Image of call numbers on books. Call numbers include: B 41 B18, BA 804 A1 H36, BF 31 M73 1995, C 31 W64 1989, CD 230 R1

Following the letters, the first group of numbers further narrows the subject. It is filed in numerical order within the letter group:

Image of call numbers on books. Call numbers include: B 53 D476 1990, B 765 L44 M67 1991, B 1201 B44 W64 1997, B 1246 R66, B 1246 R7

Notice that, for the last two books, the first group of numbers is the same. To put these books in order, the third element of the call number must be used. Treat these letter-number combinations like decimals and put them in order accordingly. It may help to imagine an extra zero at the end of the number; in this situation, placing a zero after the 7 makes it clearer that ".66" comes before ".70".

So NOW that you know how to read the call number, you can go find the book on the shelf. Go ahead, try it! Be sure to ask a librarian for help if you have any questions.

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