[Yoda]

I have a problem with your "remain vertical to" terminology. A blade is either vertical or it is not. Vertical is absolute. I would rephrase this to read "The blades of a paddlewheel remain perpendicular to their axis of rotation", if that is what you mean.

Weightshift:

You are correct in that 'vertical' means 'perpendicular' or 'at right angles to,' and I encourage you to use that term if you prefer. The term is, as you say, "absolute" in that it defines a 90 degree relationship between, e.g., two surfaces. However, that relationship can be with any given plane, not just the horizontal. Which, of course, makes it "relative."

And that is the way the term is used in TGM: Vertical (or perpendicular) relates to each of the Three Basic Planes (Horizontal, Vertical and Angled) and not just to the Horizontal. In other words, it is possible to be Vertical not only to the Horizontal Plane, but also Vertical relative to the Vertical and Angled Planes.

Do this for me:

Stand a pencil on the cover of a book laying on a table. The pencil is perpendicular -- or vertical -- in relation to the book (and its horizontal plane). Now, holding the pencil in place, stand the book upright (in a vertical plane). Though the pencil now may be said to be horizontal (in relation to the horizontal plane), it remains perpendicular, or vertical, to the book (and its now vertical plane). The same holds true when the book is tilted on any angled plane, i.e., the pencil remains perpendicular, or vertical, to the book (and its now angled plane).

Similarly, holding the Flat Left Wrist perpendicular, or Vertical, to any one of the Three Basic Planes of Motion -- Horizontal, Vertical or Angled) imparts its Motion to the Clubface. That is good news, because...

When you control the Left Wrist...

You control the Clubface.

And when you control the Clubface...

You control the Ball.

And when you control the Ball...

You control the Game.