Sure, de tuning is the name I gave it but in the manual on page 24 the official name is Narrow It Down. In case you don't have a manual here is what it says.
Narrow It Down
To further narrow the field of detection, position the searchcoil near the center of the response pattern (but not at the exact center), release the trigger, and then pull it again. Now you will only hear a response when the searchcoil is right over the the top of the target. Repeat this procedure to narrow the zone even further. Each time you repeat the procedure, the field of detection will narrow further.
Just a note from me, where it says in the manual to repeat the procedure, you can over do that process and the target will go away completely.
Okay it is time to head out in the yard with a dime for a little practice, you will get the feel for it and it is dead on.
Good luck,
Ron in WV