Great book and web presence for those who want to learn or refresh your diagnostic skills on todays vehicles. Paul gives you the theory and demonstrates the testing on actual vehicles and not by using some single vehicle but by using vehicle at the school, plus customer cars as well as out at shops around his area. Combine this with really learning how to use your scan tool, a scope and your brain and you can easily repair pretty much any electrical issue on modern cars when it comes to drivability and engine related issues. Plus much of the testing can be used for other areas as well. Highly recommend this for anyone who wants to up their skill level at diagnostics. I do however suggest getting both the book and the online version, you get updates and more testing examples that way.