So Yoda, what would the "IDEAL" downstroke plane be?
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Those Planes aligned between the Elbow and Shoulder Planes have become the most widely accepted. Clubs cannot be built to be perfectly soled and still align the Clubshaft with more than one Plane Angle Reference point, and these Planes allow the Toe or Heel to be adjusted to fit either the flatter or steeper Plane(7-6).
Specifically, for G.O.L.F.ers, the Ideal Plane would be the Turned Shoulder Plane (10-6-B). Here the Magic of the Right Forearm/Elbow Action (7-3) executes the Three Dimensional Start-Up (Up, In, and Back) and also, the Three Dimensional Impact (Down, Out and Forward) (2-F). Combined with the Downstroke Shoulder Turn of 10-13-D, this Plane Angle has a Zero Shift (10-7-A) and thus "far better performance characteristics than any other" (10-6-B).