Is it any good?

It’s a cool idea but I like to go off the actual number of pages read (starting from the proper start point of the book, not the first few pages of copyright/contents etc) so I think a general % might throw things off slightly. And I sometimes re-open older books to check annotations, so I suspect it might think I’m re-reading a book when I’m not!

If you’re not as anal as I am I imagine it’s pretty useful though xD