It's about an inch in front of the point where the shaft meets the coil. It's one of the easiest machines there is to pinpoint with.
My recommendation is to practice with some small items on the surface, in a clean area. Raise the coil off the ground a few inches to simulate depth. You should have it down pat in about 5 minutes and be ready to do it with success on in-ground items.
The graphical LCD pinpoint box is one of the coolest things about the Quattro, to me. One point that some seem to miss is that on shallower targets, the box will fill completely and be fully shaded when you are "dead on" the target. On the deeper targets, that isn't so. I've dug items that were over a foot deep that were "barely there", either in audio or pinpoint. When you get the best possible "shade-age" that you can, dig. Sometimes if it's like a deep Barber dime or similar, you may only get a 1/4 of the box to shade in...if that. You have to use a little finess, hit it from multiple angles, and make SURE you've done the best job you can getting right over it, then go with it. Does that help?