The SuDocs (Superintendent of Documents) system organizes publications based upon issuing agency. The SuDoc number or call number is based on this issuing agency.
A = publications of the Department of Agriculture,
C = publications of the Department of Commerce,
D = publications of the Department of Defense,
HS = publications of the Department of Homeland Security, and so on.
There are exceptions:
Y 1 call numbers are general publications of Congress such as House and Senate Documents and Reports
Y 3 call numbers are publications of independent boards and commissions of Congress
Y 4 call numbers are House and Senate Committee hearings and publications.
The SuDoc system is not a decimal system.The number after the point is a whole number.
i.e. - in order --- A 1.2, A 1.23, A 1.256
If the call number is the same to a certain point, then varies, the order is: Years, Letters, Numbers. Until the year 2000, the first number was dropped from years, so those years have 3 digits. Beginning with the year 2000, years will be 4 digits.
i.e. - in order --- A 1.2:999 A 1.2:D 600,
The call number stem is the numbers before the colon. If this stem has numbers slashed onto the base number, the base number comes first, followed by the slashed numbers in order. (A 1.23: is the base number)
i.e. - in order --- A 1.23: A 1.23/D:
A 1.23/D-2: A 1.23/2
An Explanation of the Superintendent of Documents Classification System (This guide has been provided by the Angelo State University Library)