Interesting fact. In the broadcast television world, with specific reference to composite analogue video signals, vectorscopes were used to measure and align chrominance levels. When measuring chroma, vectorscopes — which are essentially oscilloscopes running in X-Y mode — produce a display on which every colour in the image traces a vector. When measured against a known colour burst reference signal, the angle of that vector encodes hue, and its magnitude (distance from centre) encodes saturation. A fully desaturated grey produces a dot at the centre, while a red colour traces a long vector pointing in the "red" direction.
Equipment is aligned using a standard colour bars test signal. The vectorscope allows engineers to verify that "legal" colours fall within the 75% and 100% colour bar targets, represented as small marked boxes on the display. Each colour bar has a corresponding target box, and a correctly aligned and colour-accurate signal will place each vector precisely inside its respective box. Any deviation in hue rotates the vector away from the target, while a saturation error pushes it short of or beyond the box radially. This made the vectorscope an indispensable tool in broadcast studios, outside broadcast trucks, and post-production suites for ensuring consistent, standards-compliant colour across the entire signal chain.
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