TV advertisements around the worldTelevision advertisements appear between shows, but also interrupt the shows at intervals. This method of screening advertisements is intended to capture or grab the attention of the audience, keeping the viewers focused on the television show so that they will not want to change the channel; instead, they will (hopefully) watch the advertisements while waiting for the next segment(节) of the show. However, remote controls have now made it easier for audiences to "tune out" advertisements simply by allowing them to turn down the volume or even switch channels when the advertisement comes on. In addition, Television recording mechanisms such as DVR(放电调压器) and TiVo have also allowed viewers to skip advertising completely during television programming.Entire industries exist that focus solely on the task of keeping the viewing audience interested enough to sit through advertisements. The Nielsen ratings system exists as a way for stations to determine how successful their television shows are, so that they can decide what rates to charge advertisers for their advertisements.Advertisements take airtime away from programs. In the 1960s a typical hour-long American show would run for 51 minutes excluding advertisements. Today, a similar program would only be 42 minutes long; a typical 30-minute block of time now includes 22 minutes of programming with 6 minutes of national advertising and 2 minutes of local.In other words, over the course of 10 hours, American viewers will see about 3 hours of advertisements, twice what they would have seen in the sixties. Furthermore, if that sixties show is rerun today it may be cut by 9 minutes to make room for the extra advertisements (some modern showings of Star Trek exhibit this).Back in the 1950s and 1960s, the average advertisement was one minute. As the years passed, the average length shrank to 30 seconds (and often 10 seconds, depending on the television station's purchase of ad time), but more of them are now shown during the break, while in the '60's, only one or two advertisements would be shown at each break. However, today a majority of advertisements run in 15-second increments (often known as "hooks").
