One interesting piece of information from these sources is that the CRT displays at the controllers’ consoles did not directly display computer output. They were CCTV monitors, displaying an image from a camera. The camera viewed an optical system which superimposed a 35mm slide containing data headings over a mainframe computer CRT display which showed just the raw numbers. The Mission Control film says the system had 40 TV channels and 600 slides.
Imagine the work involved just to add or move a data field on a particular screen. The mainframe programming would have to be modified to put the data in the correct place on the correct CRT display layout, the headings would be have to be changed on the slide artwork, the slide would have to be created photographically and loaded into the display system. All of those tasks would have been done by different specialists, and it all would have to be coordinated and checked - it would not be good to mix up, say the O2 Tank #1 Pressure and the H2 Tank #3 Pressure fields on a controller’s display!