Since 1998, when Amazon.com first started tracking the sales rank of all the titles in its database, the online retailer's ranking system has been a topic of conversation in the book industry. The top 10,000 best sellers at Amazon are updated hourly, the next 100,000 are updated daily, and the rest of the list is updated monthly.

What exactly the ranks mean in real sales is unclear, but some people have attempted to work it out through guesswork and analysis. Self-publishing guru Dan Poynter estimates that a book would need to sell about 38 copies a day through Amazon's bookstore to sneak into 100th place. Morris Rosenthal of Foner Books has a less optimistic view, guessing that sales of at least 100 copies per day would be required to reach that mark, and if you were aiming for the number one position, you'd need to sell 3,000 copies per day through Amazon.com.

No matter what your Amazon rank, you can track any book's movement up and down the massive bestseller list for free at NovelRank.com. NovelRank was created by Mario Lurig to be the easiest online tool for authors tracking Amazon sales rank across the world. You can get an idea of actual sales as well as the effect of marketing efforts in near-real time.