Megan Clarken, a Nielsen executive who has been instrumental in the company’s quest to keep tabs on consumers in the many new ways they have to watch TV, is leaving the measurement giant.

“After 15 years at Nielsen, Megan Clarken will be leaving at the end of the month to take on a new position as Chief Executive Officer of another public company,” Nielsen said in a statement Wednesday in response to a query from Variety. “Since joining Nielsen in 2004, Megan has held numerous global executive positions in both commercial and product leadership. She was the chief architect of Nielsen’s Total Audience Measurement strategy, which has transformed the way the marketplace looks at content and ads across all screens finally providing comprehensive, deduplicated metrics for digital and video. We are extremely proud to see Nielsen talent reach the highest levels, and we wish Megan all the best.”

Clarken, currently Nielsen’s chief commercial officer, could not be reached for immediate comment. She was spotted participating Wednesday afternoon in an event organized by the Center for Communication, a nonprofit organization that aims to help students prepare for careers in the media industry. But she made no mention of any change in her role at Nielsen.

“If you look around the globe, all countries are grappling with how they extend their TV currency so it involves other platforms,” Clarken told Variety in 2017.

Clarken has been with the media-measurement concern since 2004, and has been among the executives working to build a new methodology of counting viewers who watch TV programs in venues other than the traditional living-room screen. Her efforts have been critical to the health of big U.S. entertainment companies like CBS, NBCUniversal, Viacom, Walt Disney, Fox Corporation and WarnerMedia.

Nielsen has for decades tabulated audience of TV programs, and its numbers are the ones used in negotiations between advertisers and TV networks. As more people move to streaming video and mobile devices, however, one of Clarken’s big responsibilities has been to keep the Nielsen yardstick ahead of viewer eyeballs. Some critics in the industry have suggested Nielsen has not been fast enough. In recent months, however, Nielsen has begun to provide some limited measures of activity in streaming environments like Netflix and Amazon Prime, and has made many efforts to count TV’s dispersing audience of field. Next fall, the company intends to add measurement of viewers who watch TV in venues like offices, bars and hotels – a development that could bring a boost to sports events, news programs and daytime TV staples.

Clarken, originally from New Zealand, spent time overseeing Nielsen business in overseas markets before taking senior roles in the U.S.