Conventional chrominance-to-luminance gain and delay measurements are based on analysis of the baseline of a modulated 12.5T pulse. This pulse is made up of a sine-squared luminance pulse and a chrominance packet with a sine-squared envelope as shown in the figure below. This waveform has many advantages. First it allows for the evaluation of both gain and delay differences with a single signal. It also eliminates the need to separately establish a low-frequency amplitude reference with a white bar.

Since a low-frequency reference pulse is present along with the highfrequency information, the amplitude of the pulse itself can be normalized.

The HAD of 12.5T was chosen in order to occupy the chrominance bandwidth of NTSC as fully as possible and to produce a pulse with sufficient sensitivity to delay distortion.