Haa those are called bar-o-meters.
A small, representative set of homes has bar-o-meters attached to their TVs. These meters detect which channel/show was on. The system counts viewing minute by minute. if you watched at least about half a minute, that minute is counted. Then it estimates what that viewing would look like for the entire target audience.
So, TRP 1.2 roughly means that on average, about 1.2% of the target audience was watching that show at any given minute.
This is a gist!
I think having them in specific homes is the disadvantage is India. In US every home with Internet connectivity to receivers for satellite subscription or OTT subscription, viewership data is gathered realtime and shared with companies like Nelson for TRP calculations.
The population is much larger and is dynamic aswell since the data shared with Neilson is random sampling to pull x number of account information.

1.5k