Baseline system definition:
urban gravity-vacuum-transit,
by L. K. Edwards and R. E. Skov.

APA Citation

Edwards, L. K., Skov, R. E. (1968). Baseline system definition: urban gravity-vacuum-transit. [Washington: U. S. Govt. Print. Off..

MLA Citation

Edwards, Lawrence K., 1919-2009, and R. E Skov. Baseline System Definition: Urban Gravity-vacuum-transit. [Washington: U. S. Govt. Print. Off., 1968.

Warning: These citations may not always be complete (especially for serials).