A specialised oscilloscope which demodulates the video signal and presents a display of R-Y versus B-Y. The angle and magnitude of the displayed vectors are respectively related to hue (R-Y) and saturation (B-Y). The vectorscope allows for the accurate evaluation of the chrominance portion of the signal. Some vectorscopes can select either 75% or 100% colour bars. Make sure the correct mode is selected or the chroma gain can be misadjusted.