The film laboratory managers can charge by the footage or by time used while in lab.
In the early days of motion pictures, films were processed by winding on flat racks and then dipping in tanks of solution.
Again after processing there is a positive ready for inspection by the production representatives, usually by projection in the dark just like one sees a movie in a theatre.
The film lab thus needs various apparatus from developing equipment and machines, over measuring tools, cutting, editing devices, and printers to different sorts of viewing machinery including classic projectors.
Besides there are sensitometers, densitometers, analysers, and array of chemical laboratory items that will help maintaining a level of repeatability of operations.