Can anyone tell me how do?

Question

tv and radio stations count their ratings? And how do they know the exact number of listeners are tuning in at certain moments? Do they have a device to do those stuff?

Answer 1

They don't have exact numbers. I'm not sure about radio, but when TV stations talk about Nielson ratings, they're talking about the percentage of a sample population. Nielson is a company that puts small boxes (like a cable box or satellite receiver) in peoples' homes. Those boxes keep track of what channel the TV is on at any given time.