We know that Netflix shows such as Stranger Things and House of Cards are immensely popular, but only the streaming service itself knows exactly how many people watch its content. Nielsen, which has been monitoring US TV viewer numbers for decades, says that’s about to change, thanks to its new Subscription Video On Demand (SVOD) Content Ratings service. Netflix, however, disagrees.

Netflix has never been open to discussing how many people watch its shows. “Once we give a number for a show, then every show will be benchmarked off of that show even though they were built sometimes for very specific audiences,” said chief content officer Ted Sarandos last year.

Nielsen says it will measure Netflix’s ratings using audio recognition software in the 44,000 US homes that contain its set meters. It will also be able to give an audience breakdown of the data, which includes viewers’ ages, and provide measurements “comparable to linear television data—including ratings, reach, frequency and segmentation reporting.”

The system only works with Netflix right now, but it is expected that Amazon Prime and Hulu will be added next year. Eight major television networks and production studios, including A&E Networks, Disney-ABC, Lionsgate, NBCUniversal, and Warner Brothers, have already signed up to receive the information.

Netflix is convinced that the new service is far from precise. "The data that Nielsen is reporting is not accurate, not even close, and does not reflect the viewing of these shows on Netflix," the company said in a press statement.

The streaming site has a point. Netflix boasts over 52 million US subscribers but just a tiny fraction of them have Nielsen meters in their homes. The biggest caveat is that the service only monitors Netflix shows viewed on set-top boxes—it doesn’t measure views on devices such as mobiles, laptops, or tablets.