Monoscope
Rather than physical test cards, which had to be televised using a camera, an alternative method was to use a cathode ray tube to generate, rather than display, a video signal. Each tube was only capable of generating a single video signal, hence the name.
Essentially similar in construction to an ordinary CRT, the monoscope contained a formed metal target in place of the phosphor coating at its "screen" end and as the electron beam scanned the target, rather than displaying an image, a varying electrical signal was produced generating an image from the etched pattern.
These were fragile, but had advantages over test cards, always being properly framed and in focus. They fell out of use in the 1960s, as they were not able to produce color images.
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