Whites Prizm III and Nails

I do not have a prism III, but I do have a Coinmaster Pro which is pretty similar. Nails are an issue for any detector because once they become rusted, their conductivity brings them right in the range of US coins. Some detectors like the Minelab's do a better job at it because you can see the ferrous readings as well, but nails can fool any detector. A few things that I have noticed that will help is that when you pin point, the detector will go into all metal mode and if you go from reading a coin in discrimination mode to reading a nail in all metal mode, then it is a nail. If the reading stays in the coin area then the chances are good it is a coin. However, keep in mind while pinpointing the detector will go to the strongest signal so if there is a nail beside the coin the detector will pin point on it. Also, be sure to turn 90 degrees when you find a target because that sometimes change your readings. When you lock in on a coin, you will see the difference that the machine will show a coin in discrimination, in all metal and when you turn 90. However, there will be times where a nail or aluminum can will fool the machine.

Another thing is switching over to the DD shooter coil will help you in trashy areas because it allows you to read between the trash versus the standard concentric coil. Just keep in mind that the pinpointing function will still pull you off target to a stronger signal. When pinpointing in a trashy area with a DD coil, it is better to use the "wiggle" method" by wiggling the coil over the target and backing away from it. When the signal stops, the target is right in front of the coil.

I swing a prism 3 and I had the same issue. After a little while you will be able to figure out what the MD is telling you. Nails tend to give intermidiate signals and coins will give constant signals when sweeoing over them. I biggest issue I have is "moving targets" ill pin point it and then dig, sweep again no signal but it will signal again 4 -6" in anther spot. It can be frustrating I just use the factory setting with the sensitivity turned down to about 1/2 way. This seemed to clear the nail issue up for me. alot of the time it will tell you something is 6 -8" deep when in reality its only a couple inches, i have found more in the plugs then the actual hole. It may take a while but I can now figure out what is trash and what isnt. I tend to dig most if not all targets cause you never know. Good luck