I have no clue how amazon figures out their placement of ranks for book sales. In fact, I can see no logical connection between the amount of sales and rank at all.
A few days ago, I was listed at 185,000-ish ranking in sales. Then, a day later, with no new sales but two new book reviews, I jumped to the rank of 139,000.
I stayed there for a few days, sold more books, and went back to 185, 000. I was still there this morning. Then, this afternoon, a co-worker at school bought a copy of my book -- and my rank immediately jumped to 69, 839.
For ONE book sale?
Seriously, if anyone can enlighten me as to how on earth this ranking system has any meaning or relevancy to actual sales, I'd love to hear what you have to say.