The ground balance is multi-turn. I doesn't have stops so 9:00 doesn't really mean a lot. The ground balance pot is 3 3/4 turn pot. so turn it one way a full 4 turns, then turn it back 2 turns and you are close to center.
For air tests, I'd turn the discrimination knob to iron and turn the sensitivity into the red zone or all the way if it doesn't chatter a lot. I can't air test all of my detectors inside. Some just chatter away so I need to put a big cardboard box outside to set the detector on.
Try all metal and see what you get.
Sven has posted Cibola air tests on his web page (there is a link in his signature block). He uses a number of different settings. Vaquero should be similar. With sensitivity at 6 he gets 6 inches on a quarter. With sensitivity maxed, he gets between 10 and 11.5 inches depending on where the threshold is set. My Cibola matches his measurements.
Check your settings and see what you get. If your sensitivity is maxed, discriminate at iron and threshold is up, 8 inches may be a little low. Check to make sure you aren't testing near other metal objects or sources of interference. If in doubt, you could send it in for a check up.
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