Bill pretty well summed it up. None of us are experts and we all learn something everytime we turn on the detector and go into the field. But, let me try to explain some of the setup procedures you may want to keep in mind.
The GEB modes of this series detectors are automatic ground exclusion balance modes. AUTO GEB is just that, AUTOmatic Ground Exclusion Balancing. Even though it is automatic, you will have to set it properly to begin with.
AUTO GEB can be set in any of the GEB modes. But, you should only check the AUTO GEB and SIG BAL from the GEB/NORM mode. Whites has made that easy. When you are operating in the GEB/Disc mode, pulling the trigger temporarily puts the detector into the GEB/NORM mode. That is why you can check the balance by pulling the trigger while hunting in GEB/DISC mode. It temporarily puts it into GEB/NORM mode.
Setting the Ground Balance and Signal Balance:
The AUTO GEB toggle is spring loaded. (in the forward AIR position) To set the GB level, squeeze and release the trigger on the handle. Hold the coil in the air and adjust the threshold tuner so you have a faint background hum. Push the toggle forward to AIR until it beeps. Then, lower the coil to the ground (where you are certain there is no metal nearby), pull the toggle back to GND/AUTO TRAC. Hold the coil steady until it beeps again. You can return the toggle to the middle position, which locks the setting your ears have determined make the detector balanced. OR you can leave it in the lower position and let the AUTO TRAC update the setting to accomodate the soil. (If your soil varies a lot, you might want to hunt in AUTO. If the soil is stable, locking it in will operate with a smoother threshold and I have found a bit faster response/reset) Now, squeeze and hold the trigger again, while raising the coil up in the air. If the threshold sound decreases, that means you have some "bad ground" and you will have to adjust the SIG BAL control counter clockwise. Remember, every time you change the Signal Balance control, you must do the GND/AUTO TRAC procedure mentioned above. Finally, when you raise the coil and there is not any change in the threshold sound, you can start hunting.
If, when you raised the coil after setting the GB, you found the threshold remained steady, you can try to optimize the detector's performance by adjusting the SIG BAL knob clockwise. The idea behind all of this is to set the SIG BAL as high as you can without overloading the AUTO GEB circuit, causing erratic behavior. Typically, the higher you can operate it without making the threshold unstable, the deeper you can detect. As well, the lower the mineralization, the higher you are likely able to run the Signal Balance. (remember the bad ground scenerio mentioned above?) Again, remember, each time you move the SIG BAL knob, you have to reset your AUTO/GEB. (see above steps) Once you have found the maximum setting for your SIG BAL, and you are able to squeeze the trigger and raise the coil without causing the threshold to change, you have successfully set the GB and tuned your detector for maximum Signal balance.
Remember, when ever you change your SIG BAL, you will need to set the AUTO/GEB again. And, anytime you make a mode change, you need to pull the trigger to reset the detector's circuitry.
If you are hunting in GEB/NORM mode, you should pull that trigger every couple minutes to reset the threshold hum. That is because the GEB/NORM mode is a non-motion mode and the threshold is more likely to drift due to RFI and mineralization fluctuations.
I am a coin hunter and since our soil is moderately mineralized, I use GEB/DISC most of the time. When hunting in GEB/DISC, I can tell if my detector is not operating at peak performance because the threshold will have changed. If it has, I simply pull the trigger, (now it is temporarily in GEB/NORM mode) and raise the coil. I listen to the threshold sound. If it is stable, I keep hunting as pulling the trigger reset it. If it varies when I raise and lower the coil, then most likely the mineralization has changed and I need to readjust my Signal Balance.
TR/DISC mode:
If I were to hunt an area in GEB/DISC mode, and the mineralization was so low that I had turned my SIG BAL knob completely clockwise, (and still not gotten it to run smoothly) I could switch to TR/DISC and compensate for the low mineralization. But recognize that TR/DISC mode will not typically hunt as deep as GEB/DISC in moderately mineralized conditions. My rule of thumb is to not use the TR/DISC mode if the GEB/DISC can be tuned to handle it!
Pinpointing:
I squeeze and hold the trigger to pinpoint, as this is an all metal "non-motion" mode. If you squeeze, release and squeeze the trigger several times, it will detune the detector and allow for more precise pinpointing. However, before you resume hunting, make sure to raise the coil in the air, squeeze and release the trigger one more time to reset the detector for wide-scan detecting.
Hope this helps explain some of the ways I use my XL Pro. If you have any questions, I would be happy to try to help figure them out. HH Randy
