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Just did that hcw and the stationary point on my grip it at the tip of my left thumb (or depending how "long" a thumb you use, the middle knuckle of my left index finger)..everything rotates around that point...
If you hold a club in front of you clubhead up toward the sky and then pivot right and left you will see that the hinge/pivot point that doesn't move right or left is where your hands meet. Using the heel pad/butt end of the club will cause an artifact as it "reverses" as the hands turn over.
-hcw
Just did that hcw and the stationary point on my grip it at the tip of my left thumb (or depending how "long" a thumb you use, the middle knuckle of my left index finger)..everything rotates around that point...