APA (7th ed.) Citation

United States. Postmaster General. (1924). U.S. Postal System, 1639-1924; biggest single business in world. U.S. GPO.

Chicago Style (17th ed.) Citation

United States. Postmaster General. U.S. Postal System, 1639-1924; Biggest Single Business in World. Washington: U.S. GPO, 1924.

MLA (9th ed.) Citation

United States. Postmaster General. U.S. Postal System, 1639-1924; Biggest Single Business in World. U.S. GPO, 1924.

Warning: These citations may not always be 100% accurate.