I just checked my Amazon stats, and my author rank went up. Great, I thought, I must have made some sales! But when I checked my sales rank it's still trending down. How does that work?
It is probably like the book sales ranks on Kindle which are governed by complicated algorithms and are based on your book's rank relative to other book which have sold, over length of time since published. You will find on Kindle that your book rank may go up or down, even if you have not made a sale, because its position relative to other books has changed.
When you make your first sale on Kindle your book quickly leapfrogs other books but, over time if it doesn't sell those other books will overtake yours in rank if they continue to sell from time to time.
The author ranking shows how your book is selling in comparison to others. Out of eight million books on Amazon it shows your placement. Some books haven't sold a single copy in years and so show over one million or higher. The sales rank can show a sale but it can show it going down if it hasn't sold more recently. I still believe I sold more than five last month.I've worked with Novelrank for 2 years now and it's been very accurate. My book just went from 39 to 9 with 14 sales showing. It's back in the top ten and this is sales rank not author ranking.
Amazon Author Rank is based on sales of all your books relative to the sales of other authors. Amazon Author Rank shows how an author's books sell relative to other authors. Like the Billboard charts, lower numbers are better. An author with the Amazon Author Rank of #1 in Mystery & Thrillers is the bestselling author in Mystery & Thrillers on Amazon. Amazon author rank is updated hourly.
Found this site that made pretty good sense.
Scyoni, in the Author Central page checking sales, look to the right it will show weekly sales. Not the actual chart showing ranks, and sales but shows the weekly paid sales of paperback. It won't show kindle or ebook sales at all. Don't know why. You have to sign up with Ingrams or Neilson? to see actual sales. I think the only way to know for sure about ebook sales on Amazon is to put them in KDP as some on here have. I haven't because they won't use Paypal and I don't like banks.