Great book, scratch that, fantastic book.  Compared to my HJ Pain Waves and Vibrations book, it's absolutely incredible.  The author goes through each step clearly, and as well as explaining how he does it, explains why he does it.  So many books today just give derivations(HJ Pain) and never actually explain why they do them.  A must have if your into thermal physics, or if you need it for a class.  Probably the latter.