The 3D won't dis' out Zincs, as it moves Zinc cents (and IH cents) up to the High Coin slot. Also, newer, modern Nickels that haven't been in the ground very long will register as a pulltab. Old Nickels will register as Nickel.
In Salt mode, the detector acts exactly like a CZ-5 in Salt mode. You can Disc' out Zincs, and modern Nickels come in at Nickel, and the older Nickels start to fall down to Foil.
Airtesting doesn't really work with the 3D, as it's designed to search for signals in a dirt matrix, and doing an airtest changes the resulting conductivity a bit.
HH from Allen in MI