A few hours ago I finished writing Chapter 10. Looking at the time on the calendar, it didn't take too long, about a month. Looking at it from the point of view of effort involved, I feel about as tired as if it took three years.
Other chapters took longer, but didn't take out quite as much effort. Not sure what this means... but I am happy I am done with it (for a given value of done, I will still need to review and read it at least three dozen times).