Hey Foxhunter,
I've owned a Delta 4000 for three years now. The coil wire at the control box pushes in and has a metal thread lock ring to keep it in place. The notch function will notch out everything but, I believe the highest three coins. (.25, .50, & $1) you can pick and choose each of any of the prior and notch them completely or hold one or two, for example keeping nickels in the series if you want a shot at gold, pull tabs, and nickels. As far as tones go, AM (all metals A-1 and A-2) is limited to 2 and Discriminate has three. When I first got the machine I used AM 2 almost exclusively. Now I mostly use Discriminate with the V.I.D. starting at 30 to 40, or eliminating iron and all low scale hits. You can still pick up an iron object even in that mode but it has to be fairly large and close to the surface. Mostly that will overload the machine and you'll know. I learned to slow the machine swing down in Discriminate and let the tones tell me what's what. I found my 1st 44 Mercury that way which was about 1" from a pull tab. It's a very good machine. But it is a beginners machine. It does hit on silver very well. Even to the point that I dug a .925 sliver lobster clasp at over 6" in a ball field once. If you get it good luck. It'll keep you busy hunting for a while.