SuDocs Classification System
It was developed in the Library of the Government Printing Office (GPO) between 1895 and 1903. Classification numbers are assigned based on government organization authorship.
In libraries, publications of the U.S. government are usually assigned call numbers based on a special classification system created by the U.S. Superintendent of Documents. SuDocs call numbers begin with letters of the English alphabet. See also: government documents.
Example: HE 20.30:112/1 (January 1997 issue of Public Health Reports)