Whitman, R. B. (1920). Tractor principles: The action, mechanism, handling, care, maintenance and repair of the gas engine tractor. D. Appleton and Co..
Chicago-referens (17:e uppl.)Whitman, Roger B. Tractor Principles: The Action, Mechanism, Handling, Care, Maintenance and Repair of the Gas Engine Tractor. New York, London: D. Appleton and Co., 1920.
MLA-referens (8:e uppl.)Whitman, Roger B. Tractor Principles: The Action, Mechanism, Handling, Care, Maintenance and Repair of the Gas Engine Tractor. D. Appleton and Co., 1920.
Varning: dessa hänvisningar är inte alltid fullständigt riktiga.