Kell Factor

The Kell Factor reflects the fact that details in a television picture may fall in between scan lines or across more than one. Multiplying the number of lines by the Kell Factor tells you the vertical visual Resolution of the picture. For a standard CRT the standard figure is 0.7, meaning a standard NTSC television has a vertical visual resolution of 338 lines (483 x 0.7), while a PAL television's vertical visual resolution is 403 lines (576 x 0.7).