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How does the Dewey Decimal System work?

The Dewey Decimal Classification System

10 Main Dewey Decimal System Classes

    000 Computer science, information & general works

    100 Philosophy & psychology

    200 Religion

    300 Social sciences

    400 Language

    500 Science

    600 Technology

    700 Arts & recreation

    800 Literature

    900 History & geography

Melvil Dewey (1851-1931) invented this system and first published it in 1876.

In many libraries all over the world, books are organized by subject using the Dewey Decimal System. With this system, if you find a book about gardening or marriage, plumbing or birds, you can also explore others on the same topic that sit next to it on the shelf. 

Dewey first ordered subjects into ten main classes. Within those classes, specific numbers are used for more exact topics. Librarians can build a number for even a brand-new subject by following this system, which is revised from time to time to reflect new understandings and new ideas.

In the Humboldt County Public Library System, a Dewey subject number label is placed on the spine of each nonfiction book, and books are shelved in order by number. When several books sit next to each other with the same subject number, they are put in alphabetical order by the name or word after the number on the label. At the end of each shelf, a sign tells you a number range for all the books that sit on that shelf.

See more details on each of the ten classes on Wikipedia. 

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1. I found a book in the online catalog. Now, how do I find it on the shelf?
2. Some of these Call Signs look like a code. How do I know what they mean?
3. How does the Dewey Decimal System work?