[Yoda]

So the motion is always PERPENDICULAR (Geometry. meeting a given line or surface at right angles) the Left Arm but Vertical to the selected Basic Plane of Motion?

How about this, Bucket:

The Left Wristcock Motion (the Plane of Motion of the Clubhead) is Vertical (or perpendicular) to its directly opposing Plane. Again, this is the same motion used when hammering a nail into a floor (horizontal plane), a wall (vertical plane) or a pitched roof (angled plane).

This Motion is sometimes Vertical to the Plane of Motion of the Clubshaft (Angled). It is always Vertical to the Plane of Motion of the Clubface (Horizontal, Angled or Vertical).