Public librarians use Dr. Dewey’s classification many times during the day. It is one thing to know we have the book, but quite another to be able to find it. The Dewey Decimal System makes this much easier. His system is the one that most customers are familiar with, and it is used in over 200,000 libraries worldwide. Dewey published his system in 1876. It continues to remain up to date with the 23rd revision published in 2011. Dr. Dewey did the revisions himself while he was alive.
Ok, you have arrived at the Library, and you need to find some information about World War II. So, you go the computer, enter WWII, and up comes this number. You write down this random, seemingly meaningless, number on a piece of paper and head off into the stacks to find. When you locate the number and your book, you notice that the other books around it also appear to be about WWII. You assume that the number somehow indicates books on WWII, but you have no idea why. Nor do you probably care. You just want to get your book.