Digger,
The 'bobbing' method works the same whether it is a CZ20 or 21. Set the unit to Autotune ( ie. All metal mode). Set the GB at 10 .Sensitivity at max, volume high enough so you can hear the threshold. Begin lowering and raising the coil off the ground from ( start at a height of about 1/2 inch off the ground and raise the coil about 10-12 inches off the ground) and keep repeating this motion ( similar to plunging a toilet or churning butter ( not my analogy...got that from another forum detectorist and it's a pretty good one).
As you continue to raise and lower the coil in that motion ( not too fast, not too slow), slowly turn the GB knob from 10 to 9, etc. as listen to the threshold. The idea is to get the threshold to NOT change as you raise and lower the coil. When you start the process with the GB at 10, the threshold may rise as you lower the coil to the ground ( or rise as you raise it). You have to try to get the GB to a point on the knob where there is minimal if any rise in threshold in both directions when you raise and lower.
Sometimes you may not be able to get an exact GB, and sometimes you may not get anything at 10 or 1 on the GB knob,. If so, leave the GB at 5.
I have a CZ20 and 2 CZ6a's and there are lots of times I cannot GB at the beach and I just leave it at 5 and there are no problems. Still runs super deep and super stable. The main thing with the CZ's is to make sure you don't run the sensitivity too high and get lots of falsing or high tones on iron. The CZ's still run deep at lower sensitivity settings.
Just remember if you are going to hunt in discriminate mode and you switch from Autotune to Discrim setting 0 or 1 ( of whatever you are going to use), make sure you lower your sensitiviy because it's at it's highest setting. If you don't you will be falsing like crazy.
Also, you can get the manual off the net.
JC
