a) In NTSC systems, video black is typically 7.5 IRE above the blanking level. This 7.5 IRE level is referred to as the black setup level, or simply setup. b) The ratio between reference black level and reference white level, both measured from blanking level. It is usually measured in percent. Black level reference expressed as a percentage of the blanking to-reference-white excursion. Conventionally 7.50% in system M, conforming to ANSI/EIA/TIA 250-C. Conventionally zero in all other systems where blanking level and black level reference are identical.