This will explain how John Crane came up with his frequencies. Those are commonly used frequencies. Is the video absolute proof? NOPE. It just shows there was a "method to the madness" in deriving frequencies. http://www.youtube.com/watch?v=U8---nRi6vU
Are zappers a "cure-all"? NOPE and John Crane himself knew they were much less effective than Rife's original work. Zappers are easier to use and make than true Rife equipment. Add in the discovery by Hulda Clark that 100% positive offset is the best method and that's another step in the right direction. Btw, Crane used both foot pads and handhelds and he still said it had limitations on reaching every area of the body. But it's simple and can help. It's not a "Cure-all".