How do TV networks know how many viewers they receive?

Question

For example, NBC states that they received approximately 34 million viewers for the Beijing Olympic opening ceremony. How do they know?

Answer 1

Surveys,

Professional Statistics and Informatics Devices, such as the ones they

use for 'The Nielsen Ratings' - When they ask 'America' to let them (the networks)  collect data on what they watch in 2 months out of the year:  Usually February and November, to gauge what's popular and what's not.

That's why (The Nielsen's) are usually good for your favourite show's storylines picking up and being great during those months,

but yes.. they have their ways.. here:

http://www.ndparking.com/nielsenratings....

Answer 2

Now that everything is so technical, digital and such, I'm sure they have devices that can tell how many television sets are picking up their frequency, or satellite signals.

Answer 3

There are a team of researchers who are expert in this issue, first of all they consider at most how many people are able to watch them that is a big number then they do an experiment that shows what sort of people watch their TV channel, kids young or old, educated or uneducated,… then they have got gross audio ness number after that by reports that come from their journalists crew they can guess approximately that is so inexact number mostly overestimated.