content: Backed into finding out about this book through the reference section in a Hemisynch/Holosynch Brain entrainment audio article. This is a great reference even though it is over twenty years since the last printing. I have just ordered another copy to ensure that I'll always have one around for reference. Superb job of covering the material. Yes the pictures are dated but, if you use this book as a starting point, the techniqes and machines that he discusses are still available and the staying power validates some of the viability of the techniques/instruments. I am on my second time through it because it is a lot to absorb and it is a compelling read.