Silver has consistently rung in at 38 on my machine thus far, I have had a couple of bouncers (jumping back and forth from 36-38 ), but I'm assuming they were on edge. The two half dimes and reale also rang in at 38, but I think because they were all in the same hole the signal was crisp. My buddy found a capped bust half dime 3 weeks ago and we always cross reference each others target prior to digging (he has an excaliber) that way we can both understand our machines better, plus its fun to guess what it is and see who's right. Anyway, he had a faint signal on his half dime and when I swung the target it was choppy, a bouncer from 32, 34,38. To be honest I may not have even dug it, signal was only one way and I figured from past experience it was probably a square nail. It was down about 12" and you know how small those things are. I've found air testing to be pretty unreliable. So I guess the only answer I can give ya Ray is that if its past 6-8" deep it may not ring at 38.
I will say this, I love this machine, I hated for the first 2 weeks and considered sending it back or selling it. Now a couple of months later and digging LOTS of targets I can determine fairly accurately what to dig and what not to dig. Knowing that makes all the difference in the world, I'm digging fewer holes and getting more quality finds, I'm sure I've missed some good coins since I usually only dig good repeaters, but they're still in the ground for another day. I think the hardest part of learning this machine is that it makes a lot of sounds, I'm more or less a coinshooter so I use Andy Sabisch's custom coin mode setting and if its a 14,32,34,36, or 38 I'm a digging fool. The nice thing about using his custom setting is you still get the brass, buttons, musket balls and other relics without dealing with the iron.