This is how they are calculating it. You have to do it manually by tracking total sales for each book and taking the ratio.
This is how they are calculating it. You have to do it manually by tracking total sales for each book and taking the ratio.or are they approximated read through rates e.g. Sales of Book 2 equal 65% of Book 1 sales, and an assumption is made that all people purchasing Book 2 have already purchased Book 1?