When a Kindle book is less than $7

I first spotted this book offered in the Kindle format at $6.71. Then it fell to $6.05 and stayed there for longer than I could remember. I just checked again and it is now $9.18

Perhaps when the price goes below $7, you must decide if you want to buy and keep it to read later. Problem is it is very easy to buy a ton of books which ended up not read.

The Elegant Universe: Superstrings, Hidden Dimensions, and the Quest for the Ultimate Theory

http://www.amazon.com/dp/B001P7GGRS/ref=...

A new edition of the New York Times bestseller—now a three-part Nova special: a fascinating and thought-provoking journey through the mysteries of space, time, and matter. Now with a new preface (not in any other edition) that will review the enormous public recepti...