Rod Library uses the Library of Congress classification system to classify library materials. This system allows for greater expansion of the collection and is more suitable for larger libraries such as the Rod Library. Library of Congress call numbers start with letters instead of numbers. Books with call numbers A through K are on the third floor of the library and books with call numbers L through Z are on the top (fourth) floor. Exceptions to this are the materials in the Youth Collection (third floor) which have Dewey Decimal classification and materials in the Documents Collection (second floor) which use the Superintendent of Documents classification system. Documents call numbers also begin with letters but they may be distiguished from Library of Congress materials because documents contain a colon in their call numbers.