How do tv ratings work?

TV series: How exactly does the 'sweeps week' or 'Ratings Period' work?

• Does advertising sold at different times of year have higher value? How is this calculated?  Do ads shown during summer TV have no value in terms of network revenue?

• Answer:

  back in the old days before cheap viewer tracking, only the sweeps months produced more detailed information for the networks. while it's still technically ongoing, sweeps are really only useful for small markets now as the large markets pretty much get detailed minute by minute ratings and demo info ... and also the Tv season is now obviously not just 3 networks and not sept to may anymore so while sweeps ratings are still around - they are not that important anymore ... and yes, sumertime viewership drops but in today's world, they do have value - in a weird way, with splintering of 100 main networks, they all matter all year round but other than reality shows, the main 5 networks do not launch shows during the summer if that's something.