United States. Post Office Dept. (1968). National Zip code directory. [Bureau of Operation.
Citazione stile Chigago Style (17a edizione)United States. Post Office Dept. National Zip Code Directory. Washington: [Bureau of Operation, 1968.
Citatione MLA (9a ed.)United States. Post Office Dept. National Zip Code Directory. [Bureau of Operation, 1968.
Attenzione: Queste citazioni potrebbero non essere precise al 100%.