Professionals know that during the course of a game, the value of chess pieces change. And they use this knowledge to decide which pieces to exchange--and when. International grandmaster Andrew Soltis, the author of Bobby Fischer Rediscovered, helps pass this important information on to novices so they can benefit, too. He investigates why the traditional ''chart of relative values'' or computer analysis so often fails to explain why certain trades and sacrifices work and others just don't. All the typical decisions a player has to make, such as whether to swap two minor pieces for rook and pawn, receive detailed scrutiny. Players will appreciate the insightful analysis.