Understanding Call Numbers  
   Explains how library books are assigned their places on the shelves, using Library of Congress Classification.
   http://www.hcc.hawaii.edu/education/hcc/library/callno.html

Using Call Numbers  
   Why libraries use call numbers. The three kinds of numbering systems used the most in the United States. Common SuDocs prefixes, an outline of the Library of Congress Classification system, and a quiz on LC call number order.
   http://www.wcsu.edu/library/using_call_numbers.html