Classical Pa Kua Change fighting system and weapons is one of the top books ever written on the subject. Filled with over 188 pages of detailed information written by two of the top American masters Johnson and Crandall this is one of those must have books to be used for instruction or reference.
A huge work of gathering info regarding historical basis and different styles of Ba gua Zhang. Taking into account that the reader has some basic training in the art (thing that I appreciate in that kind of books due to the harm that could do a “you can lear a full martial art by yourself reading only this” kind of writing), it brings good and founded advice in body structure and energy work (very good mental anchors for practice).
By the other hand, you could find a lot of good anecdotes about the life of the main original inheritors of the art, and a illustrated empty hand and weapon taolu from each main style of Pa Kua Chang.
A very good book to have in your library if you are interested in deepening in the art that you are practicing.