Hello all! I'm new to these forums and after reading for a couple hours i decided to make an account as this seems to be a good community. Anyway i am just getting into the hobby after i have found my dad's old Metal detector a Compass magnum 420 VLF/TR Discriminator. I've been doing some reading and gathered that it was a a pretty good Detector in its Hay day. i have also read about some of the techniques used to get passed missing deeper targets and targets of similar frequencies such as reverse discrimination.However i'm curious as to tuning the Magnum 420 ( if the threshold even can be tuned) where the confusion comes in for me here, is the Knob is Simply labeled ''Tuning'' with Power off being All the way to the left..now is this the Threshold tuning..or the Volume tuning? im not sure how much technology has changed since the release of this detector, but any pointers or Feedback on using these slightly older detectors would be Greatly appreciated.