National Electric Light Association. (1931). Underground systems reference book (1a ed.). [s.n.].
Cita Chicago Style (17a ed.)National Electric Light Association. Underground Systems Reference Book. 1a ed. New York: [s.n.], 1931.
Cita MLA (9a ed.)National Electric Light Association. Underground Systems Reference Book. 1a ed. [s.n.], 1931.
Precaución: Estas citas no son 100% exactas.