From the Gothamist interview with Robert Caro:
But first, Caro had some questions for us: “If you’re publishing on the Internet, do you call them readers or viewers?”
Either, I think. How do you know they're reading it?
There's something called Chartbeat—it shows you how many people are reading a specific article in any given moment, and how long they spend on that article. That's called "engagement time." We have a giant flatscreen on the wall that displays it, a lot of publications do. What you just said is the worst thing I ever heard.