I never rely on these estimates, but I often check them for my own amusement. The last dozen or so books I've read, the "Reading Stats" page has tended to grossly overestimate "time to go", commonly telling me I have 2 hours to go when I've reached 80% in 1 hour.

With my current book, though, it's doing the opposite - telling me I have 1 hour to go when it's taken me 3.4 hours to get to 39% (that time count is accurate). This made me check the stats at the bottom of the current page, and they're different again, as shown in the attached images.

I know this is unimportant, but I'm curious - why do the two sets of stats show such different estimations?