Distortions involving signals in the 64 μsec to 16 msec range. Field time distortions cause field-rate tilt in video signals as shown in the figure below. Error is expressed in IRE or as a percentage of a reference amplitude which is generally the amplitude at the center of the line bar. Distortion can also be expressed as the K Factor of K60Hz. See K60Hz.

These distortions will cause top to bottom brightness inaccuracies in large objects in the picture. These distortions can be measured with either a window signal or a field square wave. See Linear Distortions.