Did They Check The Time Or Page Number?

In conversation today, somebody mentioned that during movies, she inevitably checks the time. Most movies are so uninteresting to her that she periodically wonders how long it's been.

I can definitely sympathize with that. I am similarly uninterested in so many movies that I find myself wondering how long is left. 

What I realized much later, though, is that I do something similar when I read books. When a story is dull, I check the page number. I see how many pages I've read since starting and how many left until the chapter ends. This is a bad sign when readers do that. It means that they're detached.

When you have somebody so immersed in your story that they can't believe they read that much without realizing it, that's how you know you have a winner on your hands. So seek that out as a data point. Did they check the time or the page number as they read? It's one of the most accurate ways to gauge their interest, since they don't even realize they're doing it.