Have to agree with that as I've been over spots and thought how'd I miss that but on this occasion I cleared the spot and hit it up fresh first thing in the morning , covered it fully and then went back over again with th 12. Maybee I didn't cover fully but (I geuss you've only got to be an inch out)but this is the second time that I've missed a piece with the sdc and found some more with the 12. Another piece I found today with sdc kind of shocked me as it was basically on the surface , very faint target so naturally was thinking a small piece of rust or wire. Turned out to be gold and at least twice the size of some I've found. Basically had to rub it on the coil to hear it. Run it over the 12 and could hear it easily from an inch a way. I know air test don't mean **** but I am starting to discover things I didn't know which is all a good learning curve.