Amazon bestsellng rank

One of the questions people like to know the answer to is how many copies a book sells. It used to e easy, until ca. 2009. There was an phone number you called and reached Ingram. This is a big distributor. They told you the number of books ordered. Of course, books sold outside Ingram too, but you could multiply the number by a factor and you got a pretty good idea. Not anymore. Ingram discontinued the number. So what can you do. There is the Amazon besteselling rank, of course. You can compare books. The question is, how to translate the rank into the number of copies. There is a way, here: http://www.fonerbooks.com/surfing.htm. Essentially, if you rank under 1,000, you have a bestseller. 100,000 rank is about 1 copy per day. Check your own and you will see. What I wonder is how the Kindle raking corresponds to the overall bestselling rank. I noticed that if you rank about 1,000,000 for a paperback, your ebook will rank around 100,000 at Kindle. The question is, how it convert in