Hi Guy's
No disrespect to anyone, but something needs to be said here.
First let me state I'm not a fancier of either the M6 or the CZ-3D. I don't use either as my personal unit.
Monte, with the 3D, a couple of things could have been out with it. First, it could have had something wrong with it, and when I say wrong that also includes poor setup from the factory. The other is you were using it for a site it was not designed to detect in. I know this sounds strange, give me a minute, I'll explain.
On the not working properly, it could have been a mechanical, or an electrical problem with the 3D. But I wouldn't be surprised if it was poor alignment at the factory of the unit. This is a problem with them as far as it being the detector's fault. Hitting poor on nickels may be an indication it need a look at, back at the factory. CZ's are predominately very sensitive in the low conductive range, and nickels are a low conductive item.
Just as big a problem, is
using it in a environment that it was not designed for.
The unit was designed for operation in the enhanced mode in sites older than 1950, and including sites void of a lot of aluminum foil. This is stated by Fisher in their advertisement of the 3D. Using it for modern hunting in the enhanced mode most likely will result in not so satisfactory results.
Since being in business I have had a lot of CZ's to play with, and I have yet to find one deeper or more selective that the other, between the CZ models. Of course that is applicable if there working properly.
My apologies to the 100% Whites users for having to read a Fisher info post here.