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Reading Call Numbers

Library of Congress (LOC) Classifcation System

Most academic libraries, including Waldo Library, use the Library of Congress (LOC) Classification System.

With the LOC system, each letter represents a different topic, or "class". The link above will take you to the LOC website and will allow you to click on each class and sub-class, seeing the definitions of the letters and numbers assigned to each class. Fiction and non-fiction are all shelved together with LOC.

We also have bright green posters scattered on the walls of Waldo Library to help orient yourself within the LOC classification system. If you're not sure where you'd find a specific grouping of books, such as the engineering section, queer studies, world languages, education, and more, the posters will tell you what letter each subject is assigned. 

Call numbers look differently on catalogues than they do sometimes on the spine of an item (photos in example below):

  • An LoC call number 
    • T 62 .N3x 1972
  • How it would look on the spine of a book:
    • T
    • 62
    • .N3x
    • 1972

Broken down line by line:  

  • LINE 1 - Indicates Subject

  • LINE 2 - Indicates sub-subject  

  • LINE 3 - Third line is a “cutter number” - related to author’s name or title of work 

  • LINE 4 - Sometimes there is another letter/number combination that is used to be more descriptive of the item topic. Note, this line might not always be here.

  • LINE 5 - Last line is usually publication year

  • Anything beyond that is copy/volume number


Not every item is the same. Look at the example below to see how you can find a book in the stacks, starting from the library home page.


Here is an example of how to find a book in Waldo LIbrary's General Stacks using the Library of Congress Classification System.

Let's say we want to read the book "In the Dream House" by Carmen Maria Muchado for an ENGL class.

You'll notice the call number right beneath the title, a long string of letters and numbers:

  •  PS3613.A2725243 Z46 2019  

Before venturing into the stacks to find your item, it's a good idea to break the call number down into separate lines. This is how it might be broken down on the item/book's spine, so it will help in picking the item out from the shelf as well.

  1. PS - The first line is broken down alphabetically. Find the "P" section by exploring Waldo Library, or by checking the floor maps beforehand to know which floor they would be located on. PS would come after PR and before PT.
  2. 3613 - The second line should be treated as a whole number. In some cases, the whole number will have decimals, and those should still be treated as whole numbers. So, for example, if this line were 3613.52 instead, it would come after 3613.51, and so on. In this case, 3613 would be before 3614 and after 3612.
  3. .A2725243 - The third line will vary in length and usually combine letters and numbers. You'll want to read this alphabetically as well as numerically, while treating the number as a decimal. A would be first alphabetically, and .2725243 would be between .2725241 and .2725244. It helps to look at the last number in this line and go from there. 
  4. Z46 - Not all items will have this fourth line with letters and numbers, but treat these alphabeticaly and as whole numbers, like line 2.
  5. 2019 - This last line indicates the year of publication. Not all items will have this as their last line.

Now we are ready to venture into the stacks to find our book. 

  1. A great place to start, especially if you aren't familiar with Waldo Library's layout, is to check the "Visit" page to view our floor maps, which will illustrate what is on each floor, including what letters of books are included. You will see that the PS section for books is located on the library's first floor. 
  2. When you approach the stacks, look up to the view the placards with the call number ranges on them until you find the range you're looking for. Here is a picture of the correct range for the example we are using:                                        
  3. Next you'll skim the spines of the books to read the various call numbers. This can be a tedious task, but important nonetheless. See the photo below for an example of a gathering of books and call numbers:                                                  
  4.  You may notice the title of our book is rather easy to pick out amongst the other items, but this is not always so. Sometimes, there are multiple copies or editions of a book, so it's still paramount to check the call number to be sure it matches. But the book above doesn't have a call number?? Indeed, it does, and while most items have call numbers on their spines, they sometimes have to be moved to another spot on the book itself. Such is the case with our book, see the picture below:                                                       
  5. If we compare the call numbers, you will see that we have found the right book. Hooray!