To show you the percentage of the actual book you've read.
Just had yet another book where there wasn't as much left as I thought and it drives me mad.
I was 85% last night and thought I would save the rest for today.... turns out it finished 89% and the rest is a sample of another of the author's books.
This doesn't always happen though so not like I can bank on them all finishing around 90%.
Has anyone found a way around this.