I have tried this on a few water machines and i dont understand. i can take a dime and air test it to the maximum depth it can reach, add about 2 inches to it and swing it really fast past your coil. I dont understand how it works but you can pick it up. Slow it down and you cant pick it up. This weekend i was detecting with my minelab explorer ( I know - Shame on me) but i had a target that i could barely pick up so i knew it was around 10 inches deep. I picked up the speed of the swing and it came in loud and clear. It was a penny at 10 inches. I have tried this with minelabs and Tesoros and it works but Why?????