The math world and the physics world are not consistent with one another in their naming conventions for the angles in spherical coordinates (which angle is theta and which is phi).  (see the 3rd paragraph on this page [...])<br><br>The third edition of this book follows the physics convention, but the fourth edition switches to the math convention.  This reduces the helpfulness and ability to use the book as a "quick reference" for a physics class, because one must remember to switch all of the variables any time spherical coordinates are used.  This is so annoying that I am probably going to sell my copy of the fourth edition and buy the third edition.<br><br>If you are using this book for a reference for a physics class, I would highly recommend purchasing the third edition (or earlier) unless you enjoy being really confused and creating extra, unnecessary work for yourself.