[Jeff]

Here is a simple thought experiment as to whether Tiger's driver clubhead arc should be elliptical or perfectly circular in shape, and whether two consecutive driver swings would have clubhead arcs of exactly the same elliptical shape.

To make the experiment simple, consider that the pivot center (base of the neck at C7) remains fixed in space during the downswing between swing A and swing B. Also accept that the clubhead is in exactly the same identical 3-D position at the start of the downswing in those two swings.

Now consider what factors will affect the position of the clubhead in space at different time points during the downswing. Imagine a very accurate timer that can measure the downswing action in millionths of a second, and let's determine where the clubhead will likely be located after xx/100th of a second into the downswing.

There are six interacting variables that will influence the clubhead position after xx/100th of a second.

1) The speed of rotation of the left shoulder socket around the "fixed" pivot center.

2) The exact angle of rotation of the left shoulder socket around the "fixed" pivot center. For example, in swing A the left shoulder may rotate around the pivot center at a 90 degree angle while in swing B it could be at an 85 degree angle.

3) The speed/timing of left arm rotational movement around its left shoulder socket fulcrum point which depends on the PA#4 release pattern.

4) The angle of the left arm's rotational circle relative to the left shoulder socket - relative to the inclined plane.

5) The precise timing of release of the clubshaft (uncocking of the left wrist) and therefore the precise timing of the lengthening of the left arm-clubshaft radius.

6) The angle of the clubshaft release relative to the back of the left hand. Hopefully, the left wrist will uncock perfectly in plane with the left arm so that the clubshaft will release in the same planar arc of the flat left hand, but there could be a variation of a few degrees from swing-to-swing.

One doesn't have to be a rocket scientist to realize i) that the 3-D clubhead position at xx/100th of a second will not likely be in the same precise 3-D location in swing A compared to swing B; ii) that the total clubhead arc shape will more likely be elliptical in shape rather than perfectly circular in shape; iii) that there is no fixed center of an elliptical arc; iv) that there is no necessary causal reason why the pivot center (base of the neck) should be at the "center" of that elliptical-shaped clubhead arc.

It also doesn't require a rocket scientist to realize that the i) low point of that elliptical clubhead arc may be just inside the left foot, or somewhere else - dependent on the "fixed" position of the pivot center; and that if the low point is just inside the left foot that it doesn't necessarily imply from a causal perspective that the pivot center must be in the center of the stance.

Jeff.