Well, I've experimented, two days in a row, same plug, same site. Factory reset. Loaded the earlier software version as somebody mentioned earlier.. Programmed Andy S. In the original plug the Nox will still not give a single hint there is a silver quarter therein. CTX and Etrac hit it. It is interesting that iron readings are heavy: FE25-27 CO46-47. There is a large nail in that hole, 3" from the coin, but I suspect there is also something bigger and deeper.
I played with all settings: speed, FE bias, etc. Didn't make a difference.
Other places on the same property, the nox will hit the quarter when it is alone in the hole. Adding a rusty bolt, varying angles to the coin, 3" from it, one might miss the quarter depending upon how you come upon it. Those nails somewhat mask that there is a goody in the hole, and completely drop the vdi,. but an experienced swinger will get it, if they are taking their time and overlapping swings.
For you Nox guys, I'm telling you that you are missing things as there are certain situations where silver gets totally cloaked to this machine. If I keep swinging it, I will dig anything above a 19 that is more than a couple inches deep. In this case the 19 it was giving me was an iffy/scratchy tone in all directions. Not a single blip of a high tone. So I would keep an eye out for that.
This experiment also showed that i've been right digging one way high tones, if they repeat at 90 degrees.
I'd like to keep the machine, as the mrs is interested in learning to detect, but the F75 seems a safer bet: it is light and for the kind of detecting I do, it is, imo, a superior machine.
So my experiments are done. Really a hassle hauling two machines around. If you have other quality machines, give it a try. When that machine finds silver, put the coin back in the hole and grab the nox. Every now and then you'll be like... "Wtf?"