1.   Already, many high-end television models allow viewers to program their sets to block all programs at predetermined times or block certain channels altogether.

2.   If a viewer has programmed the television to block all shows with a certain rating, the screen will simply go blank when such a show starts.

3.   Just how viewers will program their televisions to take advantage of the V-chip will vary according to the manufacturer and model, television makers say.

4.   The company also markets VCR Plus, which allows viewers to easily program video players.