United States. Post Office Dept. (1968). National Zip code directory. [Bureau of Operation.
Chicago (17e ed.) BronvermeldingUnited States. Post Office Dept. National Zip Code Directory. Washington: [Bureau of Operation, 1968.
MLA (9e ed.) BronvermeldingUnited States. Post Office Dept. National Zip Code Directory. [Bureau of Operation, 1968.
Let op: Deze citaties zijn niet altijd 100% accuraat.