Answer: Sweeps
Step-by-step explanation:
Sweeps are type of recording that occurs in certain time periods of months for collecting information about viewers habit of start watching television or listening radio , stop watching television or radio time, watched program information , channel numbers etc.
According to the question sweeps tend to be present when viewership numbers are gathered for annual period for the year for setting advertising rates.This helps in attaining analysis and making advertiser attracted towards that certain network.