As your sales on Amazon increase, you'll see a corresponding move in your title's Amazon Sales Rank.
Amazon's rankings show how each book is selling compared to every other title in the catalog of nearly 4 million. Updated hourly, the system assigns a unique rank to each book relative to each other title's sales--the top-selling book is ranked 1, and the slowest-selling book is ranked over 3,500,000.
The closer you get to 1, the more often your book appears in Amazon recommendations. For this reason, many entrepreneurial authors and publishers concentrate on driving as many sales as possible to Amazon during a book's launch. Enlarging your book's footprint on Amazon can pay dividends for years to come.
Your book's Amazon Sales Rank is public evidence of how successful your book is. Many booksellers, publishers, and agents pay close attention to Amazon ranks. So if you manage to pump up the sales rank of your book, it can prompt brick-and-mortar stores to order more copies. Publishers looking for a complementary title might ask you to write the book for them.