NYT article on Amazon rankings

I'm asked all the time by authors, "Fine, my ranking is good.

But how many books have I sold on Amazon?" Unfortunately that's hard to determine. But the article below
explains it better than I can. (copy and paste this link into your browser)

http://www.nytimes.com/2007/08/06/business/media/06rank.html?ex=134...

(You may be asked to register with the NYT before being able to read this article.)