Não informado. (1968). Professional Engineer. National Society of Professional Engineers.
Chicago-viite (17. p.)Não informado. Professional Engineer. Jersey City, NJ: National Society of Professional Engineers, 1968.
MLA-viite (8. p.)Não informado. Professional Engineer. National Society of Professional Engineers, 1968.
Varoitus: Nämä viitteet eivät aina ole täysin luotettavia.