This is a feature in many iOS readers (Quickreader, Marvin) and Kindle Fire that I really yearn for when reading on my computer. I'd like to be able to start a timer for Calibre to measure my reading speed by recording the time and counting the number of words on the pages that I pass before hitting stop.
From this we get a few useful reading statistics
1) Reading speed in Words Per Minute (WPM)
2) Time to end of chapter
3) Time to end of book
This video shows what I'm describing, you simply press the start button at the start of a page, read however much you want, and then press stop at the end of a page and the WPM is taken care of:
https://youtu.be/37YDgxad_NQ?t=3m1s
And here is Kindle's reading time estimate statistic:
http://images.cdn.stuff.tv/sites/stu...features-1.png
I love these features on my mobile reading apps. For some reason this seems to be lacking on every desktop epub reader I've tried.