The IRE unit, unique to measuring analog video amplitude, is directly convertible to volts. There are 140 IRE per volt. The brightness represented by a video signal ranges between zero and 100 IRE. The sync pulses representing the start of a new video field (vertical sync) or horizontal scan line (horizontal sync) extend to -40 IRE. Color saturation in a picture also effects a video signal's amplitude by the addition of a 3.58MHz for NTSC or 4.43MHz for PAL color (chroma) subcarrier signal to the brightness (luminance) signal.