Dual Hinging?
 

If the left shoulder controls one of three hinge choices (horizontal, angled or vertical), help me understand *Dual Hinging*. ?? Is the 2nd hinge pin in the left wrist? (Edited additional info: In section 2G, 7th paragraph "Dual Horizontal" and "Dual Vertical" Hinging are mentioned "relative to Clubhead Travel. As I re-read this, I presume the dual reference was to backstroke turn & downstroke rotation??).

Dual
 

See his machine in 1-L.
The machine (1-L) takes two hinges to allow for the on-plane motion of the clubshaft. "Dual" means the use of two hinges creating and allowing for an on-plane clubshaft motion.

OK, MikeO, I can perceive the need for two hinges for clubshaft on-plane motion..., but when thinking of the golfer's body as a machine it helps me to imagine exactly where the hinges are suppose to be located for movement execution. Can you help me with these locations?

There is no one body part that identifies each individual hinge. The "Golfing Machine" 1-L merely describes the abstract principle at work.