Think of it as being two pickups in one casing. One knob does one bit, t'other the other. Plug in to the amp, turn both volume knobs down to zero. Play summit (no, s'not loud, I know...). Now turn one knob up to halfway, and play some more. Turn it back down, and do the same with t'other knob. Any difference..? While this second knob is turned up, gradually turn up the first one, so that they're both working. Any difference..? Try it, and any other combination that takes your fancy.