When you get that null, switch screens to a completely open one. The null should turn to a grunt (iron). Like Dave said, the hardest ones are the nails that false a high tone. Makes you really want to dig them. :lol: But I suggest trying to guess what the target is going to be and then digging them to see if your correct. Do this until you get the difference between iron falsing and a real non ferrous target. One of the things I liked about the E Trac was that it could detect a non ferrous target while the iron next to it was nulling.