Pivot center

[Yoda]

Yoda - you wrote-: "To maintain the Point of Compression (2-C-0) through Impact and for consistent Directional Control (2-D-0), there must be a Centered Arc. Or, a "compensating manipulation". In turn, a Centered Arc requires that both the Pivot and the Arm/Clubshaft Swing be Centered. In other words, the Pivot has its Center, and the Primary Lever Assembly (Left Arm and Club) has its Center. They are not the same."

I can understand that there are two centers of rotation - one for the pivot's center and one for the arm/clubshaft's center, but you have not explained why they both have to centered between the feet to create a centered clubhead arc.

First of all, the left arm/clubshaft has a fulcrum point at the left shoulder socket joint. However, the clubhead does not circumscribe a perfect circle around the left shoulder socket (because the clubshaft has an angle relative to the left arm that varies from 90 degrees at the start of the downswing to 0 degrees at the low point).

Secondly, the left shoulder socket has a variable relationship to the pivot center (base of the neck) during the downswing.

It's like there are two intersecting circles of rotation - left shoulder socket relative to the pivot center (where the radius is likely to be constant) and left shoulder socket to the clubhead (where the radius is constantly changing). These two circles are moving at different speeds in the downswing, and hopefully, the clubhead arc will end up being relatively circular (actually more likely to be slightly elliptical) with its low point ending up a desired distance ahead of the ball position. So, for example, if the ball is placed 4" inside the left foot, then the low point needs to be "x" inches ahead of the ball position. However, in this model - there is no necessary requirement regarding the two circles of rotation (that are both in constant motion) that the pivot center must be perfectly centralized in the stance.

Here is the downswing clubhead arc of Aaron Baddeley's swing.



Point "X" is the low point of the clubhead arc. Note that the pivot center (base of the neck) is not centralised in the stance.

Here is the downswing clubhead arc of Tiger Woods swing.



Note that the clubhead arc is elliptical. Note that the low point is at the ball position. Note that Tiger's pivot center (base of neck) is not centralized between his feet.

Jeff.

"WhhhoooooWWAAAHH!!! Have mercy! This thang's killin' me!"

[BCGolf]

In 2-H Mr. Kelley wrote, ‘Though the “Head” Pivot Center is recommended, it is not at all mandatory. The important thing is that the true Swing Center for ALL COMPONENTS is around a Hinge Pin with one end at the top of the Stationary Head and the other in the ground, precisely between the feet, with no regard for Body Location or Position at any time.’
You can move your head if you choose to but what advantage is it?
Why not keep it stationary?
It is too bad that Gulbis, Creamer, Woods, Baddeley and others do not set their head at impact fix.

[mb6606]

In 2-H Mr. Kelley wrote, ‘Though the “Head” Pivot Center is recommended, it is not at all mandatory. The important thing is that the true Swing Center for ALL COMPONENTS is around a Hinge Pin with one end at the top of the Stationary Head and the other in the ground, precisely between the feet, with no regard for Body Location or Position at any time.’
You can move your head if you choose to but what advantage is it?
Why not keep it stationary?
It is too bad that Gulbis, Creamer, Woods, Baddeley and others do not set their head at impact fix.

Yes and why did Homer choose the stationary head? Because he used his eyes focused on the ball as the easiest way for the golfer to determine if the head was stationary or not.