Netflix tracks shows by measuring "starters," "watchers" and "completers"

The Verge

A letter that Netflix sent to the British government offered some insight into how Netflix tracks viewership. Starters are “households that watch two minutes of a film or one episode” in a series, according to Netflix. Completers are “households that watch 90 percent of a film or season of a series.” Meanwhile, households that watch 70 percent of a movie or one episode in a series are considered "watchers."