The first letter, or group of letters, in a SuDocs number indicates the department or independent agency that created or issued the document. The number before the period indicates the issuing bureau of that agency, and the number following the period indicates the type of document. So the stem, or class number, for this example tells us that the item is a national parks information circular, about a national river, from the National Park Service, which is s part of the Interior Department. The book number can be based on the main word of the title, the series number or issue number of the document. Since it is an information circular about the Buffalo National River, Buffalo is the main word in the title and a B is used to start the book number.
Some documents are journals, works in a series, or annual publications.
Often, these items will have book numbers that have no letters in them. Instead the book number will use the three digit number to represent the year of publication, or will use an issue and volume number system. It is important to remember that unlike the Library of Congress Call Number, which the library uses for its main collection, all numbers are whole numbers in a SuDocs call number. Exception - Even though all numbers in a SuDoc Number are whole numbers, there is one instance where they are not shelved in numeric order. Often, when new editions are created, a slash and a three digit number are added to signify the print year.