I think the manual must be wrong. The way I GB mine is to set it in Auto Tune, turn up Sens all the way and volume too. Bob the coil up and down slowly while adjusting the GB knob one way or the other till the threshold is the same tone up as it is near the ground. When it is, turn down Sens. and Volume and if you want to hunt in Discrimination, turn it to 0 or 1. I always had trouble using the push button method to ground balance.