This is a great scale book for guitarist and one that I refer to often. I still haven't found the ONE perfect scale book (hence only four stars), but this one comes close. It is one of three scale books that I use, and because of its compact size, it is usually the one that I have handy when I need it. Troy does a great job of explaining the scales and giving some exercises for practice. What I like best about this book is that it shows the scales in all positions across 22 frets with the root notes highlighted. Also, many scale books only show fretboard diagrams of the scales in one key, usually C or E and then explain how to move them around. This book includes diagrams of several keys (including G and A, which are favorites of mine). The only other thing I wish about this book is that it was spiral bound so it would lay flat when open, but I would rather have this book than any of the other gig bag sized ones that are spiral bound. All in all a great little scale reference and cheap too!