Noticed something confusing as I was reading a book on my Kindle app on my iPhone. Even though I was on page 229 of 263, the bottom of the app said that I was only done with 64% of the book. I did the math and confirmed that, according to my page position, I was actually done with 87% of the book. 

Was this a bug? Well, not so fast. The other data point being displayed is location. And according to that metric, I was at location 3946 of 6164, which turns out to be 64%. Based on what I can see, it looks like the key difference between page numbers and location is that page numbers start and stop based on the actual book content while location includes everything — even the table of contents as well as the acknowledgments and index at the end of the book. 

As a user, when I see the % complete statistic, what I really care about is how far I’ve come so far, and how much longer I need to go to finish the book. Thus, this metric should be based off of the page percentage and not the location percentage.