Every book in the library will have a call number on its spine or on its front cover. Call numbers are a combination of letters and numbers that tell us a great deal about the subject matter of a book. In general, call numbers have four lines. Each line tell us something different. Here is an example of a call number:
All call numbers actually begin with one or more letters. These letters are assigned based on the book’s subject matter. This library is filled with K call numbers because K is assigned to books about the law. The example you see above has only one letter in the first line, K. But there may be as many as three letters used to narrow down the subject matter. A book about the law in Iowa would have a KFI call number.
On the second line of each call number is a whole number that further describes the subject. One of the most frequently used numbers on the second line is 1. This call number is used for periodicals. The call number for ABA Journal begins K1, for example. The whole number in the second line may be as small as 1 or as large as 9999.
.A55 ← The third line of this call number is .A55
On the third line there will be both a letter and numbers. Both represent the author’s name. And this number should be read as a decimal. Therefore K1.A55 would come before K1.A6
Not all call numbers have a fourth line. If they do it will often tell us the book's year of publication. And there may be a volume number (v.1) and/or a copy number (c.2).