rockpup1 --
Several things. First, the Gold Bug Pro and Gold Bug DP are exactly the same machine -- precisely the same, only difference is the Pro comes with the 5" DD coil as its "stock" coil, and the DP is a "Pro" but comes stock with an 11" DD coil. That's it. Buy a DP, and put the 5" coil on it, and you have a "Pro," and vice-versa.
Settings? Very simple on this machine. One knob -- your threshold knob, determines if you are hunting in discrimination mode, or all-metals mode. If you "click" the button by turning it all the way counterclockwise, you will "click" into disc. mode. If you turn it clockwise, and "unclick" it from disc. mode, you enter all-metals mode, and turning the knob farther in the clockwise direction turns up your threshold (which you will see on the digital display -- threshold numbers going up). The other knob is your sensitivity -- which also shows up as a digital number on the screen as you adjust it. I am most often, in my experience, able to run it near or at maximum sensitivity (100).
You can do an automatic "ground balance," and while in all-metals mode, you will get a continuous digital readout of the ground phase. If you want, you CAN adjust the ground balance manually, setting it whereever you want above, or below, the ground phase reading. So, in summary, you CAN INDEED do both types of ground balancing -- manual OR automatic.
You will probably nugget hunt in all-metals mode (unless in a highly nail-infested site where you may want to use a little discrimation). The machine is a deeper, more sensitive unit in all-metals mode versus in disc. mode.
Hints on operation? It's a very, very stable unit. It likes a faster sweep speed. A good way to coin hunt is to set the "tone break" at 40, which is at the top of the iron range on this unit. Setting the tone break here will allow all below 40 VDI (iron) to give a low tone, while above 40, all targets will give a modulated, VCO audio tone. However, like I say, if you are not coin hunting, you will probably be in all-metal mode anyway, where all targets will give modulated VCO audio reports. It's about as simple of a machine as I can imagine, in terms of user-friendliness, but is VERY sensitive, VERY powerful, VERY light, and fun to use. It is designed primarily as a gold machine, and so you will be using it for its most natural purpose -- prospecting. It is sensitive on gold (19 kHz frequency), and I can even hit a 1/10 oz. nugget (though not very deep). Larger nuggets, obviously, will hit progressively deeper.
You will, I think, really enjoy this machine. Let us know if you have any more questions.
Steve