Amazon sales ranks have become a surrogate for measuring actual sales online. When Amazon says a book ranks 2,000 it means it is the 2,000 besting selling book that hour; it doesn't tell you how many were sold. In fact often a few copies sold can move a book's rank, depending on time of day, week, or the rest of the world of books. (Use this chart to make a rough correlation between rank and copies sold if you really need to know.) Nonetheless, because these ranks are public (unlike bookstore sales) and easy to grab, they have become a great way for anyone to monitor how a book is selling. In the past it might take 6 months before sales of books were reported. Now authors and publishers with new books will check hourly to see if their rankings have been improved by a radio interview, or book review.

But you don't need to be the author or publisher to have an interest in how a book is selling. Trendspotters long ago discovered that books are good canaries of ideas, and that monitoring clusters of books gives you a zeitgeist reading, very similar to Google's Hot Trends, which monitors search terms over time. Also keep in mind you can track other things on Amazon besides books: CDs, games, software. You just need Amazon's ID for each item.

While you can just check the Amazon page to see what a product's ranking is, what you really want is something that constantly tracks an item and compiles the data into graphs, charts, and spreadsheets. There are several websites that do this. I previously recommended JungleScan, the original Amazon tracker, for a free way to track Amazon rankings. The site was abandoned last year (although its owner says he will revive up "someday.")

TitleZ

TitleZ is a new free site (for now), It's been in beta for years. You can track many books for free, and get some handsome graphs of their ranking. The good thing is that TitleZ will instantly give you the back history of a book's ranking back to 2004. The downside of TitleZ is that you can't export the data, or do much else.

A TitleZ track of my 1994 book, above. Below is a comparison chart of my two books in print.

RankForest

RankForest has many more features, and friendlier interface. Unfortunately, you can track only one book for free. And you don't get historical info; you have to register a book to track it. For more books, and more features you need to pay a monthly subscription, beginning at $3/month and up. Other goodies in the paid version include the option to add other online bookstore rankings, like Barnes and Noble, complex graphing options such as racing two books, alerts, and so on.