A basic ratings concept is HUTs -- Homes using Television. One can approximate HUTs by adding ratings for all broadcasters in a market during a given daypart of timeslot.

Here are some November ratings from Portland at 9 p.m. on an average Thursday. note that adding the ratings yields a sum of 52, not 61 -- the actual HUT figure. The "Missing" ratings are homes watching cable, distant stations, and VCR off-air taping. These homes aren't watching any local station, but they are using television.