The best test target if you do not have a small natural nugget is a 22 cal. slug, it is about the size of a small nugget and the sound is just like a nugget. Glue the 22 slug to a colorful piece of plastic about 1"x1" or put it in a small film canister, also a nickel mimics the same sound and has the same qualities but of course is much bigger but gives you the sound of 8"-10" deep nugget, paint it red or yellow so you can find it easily after you tune your detector. I prefer the smaller of the two because you will find that the 22 cal. slug will be the most appropriate size for the natural gold you are searching for. Just so ya know, many small nuggets/pickers will read +2 - +30 range, I have never found a gold nugget in the 0 & minus range unless it was next to a nail or piece of wire stuck down in a crevice, if you get a negative reading over a crevice DIG IT!!, a good portion of the time it will be a nugget with some type of iron very close and I have even found coins like this. I hope this info helps.