Swing your coil over a nickel, then turn up the disc. knob a bit at a time until the signal cracks and the nickel drops out. Mark that spot. Do the same for tabs and zinc pennies. Then, when detecting, if you have a signal above the nickel mark, it's probably a tab, copper or clad/silver coin. If the signal is lost at the tab mark, then the odds are good it's a zinc penny, copper penny, or silver/or clad coin. If it's above the zinc penny mark then - well you see how this works. With practice, this gets to be pretty accurate although you'll still be fooled by some junk targets occasionally. Remember that gold jewelry is discriminated out by or before the nickel setting and sometimes will even read as a zinc penny.
With practice you'll get to where you will often have a pretty good idea whether it's junk or likely a good target by the tone, even though you're using a single tone machine. I can often make a guess that a coin is probably a quarter and often be right, but I doubt that I could TELL anyone else how - after hours of detecting, I just started recognizing very subtle differences in the tone.
Hope this is helpful,
luvsdux
