Nielsen Rating System

We collect viewing information for both national and local programs — not only what's being viewed (tuning data), but also the composition of the audience (demographic data).
Daily household minute-by-minute viewing and tuning data, from both the national and local metered samples, is stored in the in-home metering system until it is automatically retrieved by our computers each night. Once the data is relayed via phone lines to our operations center in Oldsmar, Florida, it is processed that same night for release to the television industry the next day.
Television networks, stations, and third-party data providers give us information on program lineups, telling us what aired on each channel. This essential reference data helps us turn the raw tuning and viewing data into meaningful numbers for reporting.
To comprehend the dimension of our task, let's look at the numbers. We collect information from approximately 25,000 metered households starting at about 3 a.m. each day, process approximately 10 million viewing minutes a day, and make more than 4,000 gigabytes of data available for customer access the next day.