In this blog post, I’m going to tell you how libraries use the decimal point/period to properly organize books, versus the previous uses you might remember. In math, the decimal point helped you know how large a number is and what numbers to pay attention to when rounding. In grammar a period can mean the end of a sentence, is used after Mr. or Dr. to signify a title before a name, and is used in web addresses before com, org or net.

Regarding how libraries use this punctuation, most of you are probably wondering what I am talking about. Some of you are probably saying: “What? Don’t you use the author’s last name to organize your books?” Well, those of you who said that are actually right. To those who didn’t know, now you do. However, I am referring to the way libraries organize their nonfiction section.

The non-fiction section of a library is full of all the books that are not fantasy. It includes books written by authors about a real topic, event, theory, person, place, thing, or idea.

For example:

I have patrons who want’s books about dogs. However, I may need to ask them questions to get more specific.

The first question I ask is if they want books about a character owning a dog or a story from a dog’s point of view. If this is the case they want fiction books like Old Yeller or Clifford.

If this is not the case then I ask them if they want books about breeds of dogs and the characteristics of said dogs. If yes then I know they want a nonfiction book.

Next, I ask if they are looking for a specific breed like a Golden Retriever. So I look for books specifically on that breed. If not I am just looking for a book that includes all dog breeds.

Let me give you some visuals. 


I am showing you pictures of myself using the Dekalb County Public Library System. First I searched dogs. That is too generic a search and brought up everything in fiction and nonfiction.


Next I searched dog breeds. I then clicked on the book that was titled: The Complete Dog book. This gave me the Call Number: 636.71 Com.

Now we could just give the patrons this call number and have them find the books that way. However if they wanted specifically Golden Retrievers then we need to refine the search


When we look up specifically Golden Retrievers then we get the Call Number: 636.752.

This may not seem like a big number gap to you but when you are looking for books in the stacks it makes a huge difference. This saves you from having to look through a number of shelves to find what you want. This way you can go right to the books on Golden Retrievers.

Wondering what the numbers mean?

Well to understand that let’s take a step back: “The system was conceived by Melvil Dewey in 1873 and was first published in 1876” (OCLC).  This system has developed and changed a lot since then.

The system breaks down into a number hierarchy, like how the alphabet breaks down. We know that A always comes before Z and digit 0 always comes before 9.

So with numbers in the system: 151.06 goes before 607.78 however 001.64 goes before 151.06.

Going back to the hierarchy part, we start off by separating the sections into hundreds.

Each hundred refers to a different section.

000’s means Computer science, information & general works, 100’s mean Philosophy & Psychology and so on until we hit the 900’s which is History and Geography.


It doesn’t stop there, because otherwise how would the 600’s, which is: Technology, bring you to dogs?

Next, the hierarchy breaks down into 10’s. So: 100’s are Philosophy, 110’s are Metaphysics, and 120 is Epistemology.

As you probably guessed by now it breaks down further into one’s: 510’s are Mathematics, 511’s are General principles of mathematics, 512’s are Algebra, 513’s are Arithmetic, 514’s are Topology, 515’s are Analysis, and 516’s are Geometry books.    

Now here is where the decimal point or period comes in. Remember we are only working with hundreds, so the decimal point allows us to get even more specific. Therefore going from 516 to 516.1.

As the numbers increase in length, you get more and more specific depending on what you want to find.

Going back to my example, the patron wanted nonfiction books on dogs and specifically wanted Golden Retrievers.

If you couldn’t just use a computer to search to find it you would have to know:

  1. Animals are under the 600’s, which is Technology.
  2. 630 is Agriculture
  3. 636 is Animal husbandry
  4. 636.7 is Dogs.
  5. 636.752 is specifically Golden Retrievers.

By this, you also know that any other breeds of dogs are between 636.7 and 636.8 because the 636.8 section is about cats. So, like with directions, if you hit the cat-related books on the shelves you have gone too far and need to turn around.

So you see the decimal point or period isn’t just used for ending sentences, depicting someone’s title, website addresses or for simply separating two numbers. It is also used to separate types of books for easier access in a library. This way you don’t have to go looking through huge stacks of books when all you want is a book on Golden Retrievers.

Sadly most people have forgotten what the numbers and the decimal point represent due to the fact that the card catalog has been digitized. Despite the fact, most people have forgotten its meaning, the numbers and the decimal point or period between the numbers exist for a reason.  

For further information on how The Dewey Decimal System breaks down, go to Dewey Decimal Classification® summaries

All pictures were either taken from my own computer via a screenshot or was taken from Google Images under their labeled for reuse tool.

Work cited:

OCLC. “Dewey Decimal Classification Summaries: A brief introduction to the Dewey Decimal Classification System.” The Online Computer Library Center, Inc, 2016. Web. 13 Sept. 2016.

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