I've been running into the problem with my ACE 250 where I'll scan over an area, getting a few different varying tones, I'll pinpoint it, and dig, find nothing, then scan over the excavated dirt and empty hole, and the ACE doesn't even go off when before digging, it was. Even after checking the hole and dirt pulled with a pinpointer just to make sure something wasn't turned over. A lot of junk metal shows up as nickels too, but I guess that's just part of it. Its just irritating to hear varying tones, dig a hole, and find nothing, scan again, and get no tones at all after double checking.