United States. Postmaster General. (1929). Cost ascertainment: Instruction letter M; record of revenue, pieces, and weight of mail transported on domestic and foreign contract air-mail routes. U.S. GPO.
Chicago Style (17th ed.) CitationUnited States. Postmaster General. Cost Ascertainment: Instruction Letter M; Record of Revenue, Pieces, and Weight of Mail Transported on Domestic and Foreign Contract Air-mail Routes. Washington: U.S. GPO, 1929.
MLA (9th ed.) CitationUnited States. Postmaster General. Cost Ascertainment: Instruction Letter M; Record of Revenue, Pieces, and Weight of Mail Transported on Domestic and Foreign Contract Air-mail Routes. U.S. GPO, 1929.
Warning: These citations may not always be 100% accurate.