Your volume doesn't need to be at 10, either. I usually keep my volume set at 4 1/2 on the box of my CZ-5, and then adjust the volume on my headphones to where it's comfortable.
As long as you're in Auto-Tune, search around until you find a quiet piece of ground. It's not a good idea to GB underneath powerlines or near a transformer, as they put out RFI. When you do find quiet piece of dirt, start pumping the coil up and down and LISTEN! If the sounds starts soft and gets louder as you approach the dirt, you're positive (the detector sees the dirt as a positive, or good, target). It will sound like you're approaching a target in pinpoint mode. If the sound hits hard and loud, then falls off in volume and pitch as you move away from the dirt, then you're negative. Whichever one you are, you want to adjust the GB knob until there's hardly any change in sound. This is when you have achieved a good GB. I've heard that to achieve a little extra sensitivity and depth, you want to GB slightly negative, with a little bit of sound on the up-stroke. This helps pick the positive targets out of the ground mineralization.
Another tip: The amount of mineralization present in the dirt doesn't determine which number gives you a good GB. The mineralization determines how big of an arc on the knob will give you a good GB. The higher the mineralization, the less amount of "play" on the knob before you notice a change in the GB'ing. In areas with low mineralization, you can have an arc that may encompass one or two numbers on the dial that are "sweet", and will give you a good GB. In highly mineralized dirt, the "sweet" spot is really small, and may be to small to accurately hit. You can get close, but not right on it. In that case, tune the GB slightly negative. An extreme example is the sandy beaches of Florida. There is NO mineralization. The "sweet" spot on the knob is so big, that it actually encompasses the entire range of motion on the GB knob. There has been debate for years about where to set the GB knob in that situation, 0, 5, or 10. They all work.
Once you've gotten a good GB for your hunting area, turn the Sensitivity down and start hunting. Tom D. has mentioned several times that a CZ reaches it maximum depth at 4 1/2. This is optimal in trashy areas with deep targets, as you have the ability to reach down there, with little interference from nearby trash targets at the same depth. Shallow trash, however, will still mask deeper targets.
HH from Allen in OK