Chapter 7, "An Overview of the Zone System", summarizes the Zone System method of exposure and development. It answers several questions such as what if you have to shoot quickly, what about flash, and is it valid using digital technology.
Chapter 8, "Zone System Testing: Method 1", explains that once you learn the Zone System, you must test the system with your equipment, film and paper. Method 1 is derived from the more classic works on the subject.
Chapter 9, "Zone System Testing: Method 2", continues with the testing concepts, but is geared for more experienced photographers who want reliable guidelines as starting points and allow you to work from there.
Chapter 10, "The Zone System and Digital Photography", the largest chapter, takes what we have learned about the Zone System and now applies it to digital photography provide a clear and simple method for obtaining the best possible quality in your photographs while providing a broad understanding of the concepts that underlie digital image processing.
Appendixes A-U, cover a wide range of topics from color management/spaces, what are pixels, bit depth, film processing, contrast control, ASA/ISO numbers as well as other suggestions tips and suggested reading for more information on the Zone system.
The Practical Zone System is probably the easiest to understand book on the Zone System. It does not try to get caught up in a lot of technical details; rather it gives just enough detail to guide the reader through the basics of the system. It removes the calculations and gives you what you need to know to successfully use the Zone System.
The Practical Zone System while coming from a traditional film based methodology; Johnson tackles effectively the use of the Zone System within the digital world. In the book he remarks that Ansel Adams predicted the eventuality of the digital image as early as 1984 and that if he were around for it, he would have embraced it as he did every other photographic technology.
I have to recommend The Practical Zone System for anyone who wants to go deeper into the photographic method in an effort to get more professional results from your images. While you may not use the Zone System to take all of your photos, the knowledge will transform the way you work.