Some folks may refer to this as the iron meter. Here's a tip. When you get over a target be it shallow or deep, DO NOT look at the meter and decide the target is iron just because the meter rises some while you're sweeping target. This is a big no no. I have dug quite a few good coins (mostly deep) and the ole mineralization meter would rise while I was sweeping listening to the cat purring tone. Don't know exactly what's causes the deus to do it, maybe it sees the target as a possible anomaly. Cheers