The following lines were added (+) and removed (-):
NTSC TV sets and program material such as broadcasts and video tapes use 525 scan lines. The number of scan lines is the limit for vertical resolution, the number of dots in a column that can be reproduced. It is pretty much the same for all decent NTSC TV sets of moderate or large size.For NTSC, the picture occupies approximately 480 of the 525 scan lines. For broadcasts the portion of a scan line that is visible can hold up to about 440 dots so a grid 480 high by 440 wide represents the maximum amount of picture detail possible.