system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How can televisions measure number of people who watch them?
gpt
The television can't, but a sample of families are given boxes which track what's on TV and who is in the room. They just press a button on a remote when they enter and leave the room. Then the company handing out the boxes (e.g. Nielsen in the US or BARB in the UK) extrapolates from their sample to estimate the total number of viewers.