The early video format was designed to fit into a fairly small spectrum, so that a number of channels could exist in the same area. The design of the signal was to capture and reproduce motion. The scan rate was designed to allow the home television set to use the 60 cycle from the local power for internal timing. All television sets today use very precise crystal occilators.
Early television sets had only two adjustments, brightness, which increased the total illumination of the image, and contrast which increased the difference between dark and light.