How do the Tv networks know when your watching Tv?

Question

I remember a while back on the news, I can't remember if it was the Superbowl or the Olympics, but they said about something-hundred thousand viewers were watching the show. I was just wondering how they know when you're watching Tv? Is it only for shows on their network?

Can someone explain this?

Answer 1

They use the Nielsen ratings.  There are households in the U.S. which have a monitoring device hooked up to their t.v.'s.  These households are supposed to be a representative group for the entire nation.  The statistics are gathered and they scale it to the number of total homes with t.v.'s