If I had read about this a few years ago, I would probably have dismissed it as American propaganda, designed to fool the Russians into underestimating their technical capabilities:
"How each channel was generated, though, is almost shockingly primitive by today's standards. The computers downstairs in the RTCC were responsible for producing the actual data, which could be numbers, a series of plotted points, or a single projected moving point. The System/360 mainframes generated the requested data on a CRT screen using dedicated digital-to-television display generators; positioned over the CRT in turn was a video camera, watching the screen. For the oxygen status display example above, the mainframe would produce a series of numerical columns and print them on the CRT.
The numbers were just that, though. No column headings, no labels, no descriptive text, no formatting, no cell outlines, no nothing—bare, unadorned columns of numbers. In order to make them more understandable, an automated mechanical system would retrieve an actual physical slide containing printed column headings and other formatting reference information from a huge bank of such slides, and place the slide over a light source and project it through a series of lenses into the video camera positioned above the CRT. The mixed image, made up of the CRT's bare columns and the slide containing the formatting, was then transmitted to the controller's console screen as a single video stream."
That scarcely believable description in a fascinating article on ArsTechnica explains how vital real-time metrics concerning systems aboard or relating to the Apollo space missions were generated in the back rooms and displayed on the infamous consoles at "Mission Control, Houston".
Suddenly, the quaint, amateurish almost home-made feel of the original bridge of the 23rd Century USS Enterprise appears rather more advanced, for its time, than perhaps we give it credit.