Perhaps it will help clear up the confusion if you look at the Eyeline laser and imagine it aimed in a different direction. Now, on the Eyeline demo, the laser aims down the shaft. Instead, imagine it aiming vertically at the ground beneath the end of the laser where the light beam emerges. This will project a left-right line on the ground directly beneath the laser, and this laser line on the ground will parallel the putt line, running left-right a few inches closer to the feet.
When the golfer makes a vertical-plane shoulder stroke, this laser line will STAY right where it is. No matter where on the shaft you locate the laser with this orientation straight down and no matter the angle out of vertical that the shaft extends away from the golfer, so long as the golfer moves the shoulders in a vertical plane, this laser line will STAY right where it is -- no twisting and no sliding closer or farther from the feet.
This indicates that EVERY piece of the shaft in a vertical plane stroke does exactly the same thing -- each piece moves straight back and straight forward on the same line, from the top of the handle all the way to the sole of the putterhead.
If you placed a laser beam out of the bottom of the shaft aiming beneath the sole vertically at the ground, this beam would also describe a perfectly straight line.
ANY laser line left-right aimed the way the Eyeline people aim it will misrepresent what is happening in 3D. If you implanted a laser in the base of the neck and aimed it at the ball to make a left-right line, and THEN moved the shoulder frame in a vertical plane of rocking, the laser line will twist about on the ground. If you aimed the laser with your hand held near the base of your neck and aimed it at the ball, and then rotated your hand in a vertical plane, then laser line will twist about on the ground.
If you leaned a large cone so the apex point sits against your neck and the round base rests on the ground in a single point at the ball, AND the base of the cone has its center the same height as the base of your neck (so a line from apex to center of circular base is horizontal and level to the ground), holding a stick flush with the underside of the tilted cone from apex to ball, and then made a vertical-plane shoulder stroke to move the stick back and thru, the stick would skim around the angled surface of the cone's side flush at all points back and thru. If instead of a stick, you used something oddly shaped (liked two arms and a putter), and then made the same stroke motion, there is still an imaginary stick skimming flush along the side of the cone back and thru. If you sliced this cone into infinite vertical slices (like a cone-loaf of bread) from apex to base so every slice is parallel to the plane of the base, also cutting thru the arms and putter, each slice of the cone matches one and only one slice thru the arms and putter. If you placed a handle on the side of the cone on the underside halfway between the apex and the base and "rolled" the cone with this handle using both hands so the base of the cone simply rotated, the shoulder frame would move in a vertical plane about the pivot.
EVERY piece of the whole body and the putter too moves straight back and straight thru as it traces around beneath the cone in the stroke. The PIVOT at the apex spins / rotates in place but does not move left or right (X dimension) and does not move up or down (Z dimension) and does not move closer or farther from the center of the body (Y dimension, all 3 dimensions), while the BASE of the cone moves significantly left and right (X dimension) and also spins / rotates so that the starting point on the circumference of the base that is initially resting on the ground rises going back and rises going forward of the bottom starting position (Z dimension), but there is no movement of the base closer or farther from the center of the body or the point where the base of the cone initially rests on the ground (Y dimension). The vertical-plane stroke ELIMINATES the Y dimension in every aspect of the motion, from the center of the body all the way to the bottom of the putter sole.
Cheers!
Geoff Mangum
Putting Theorist and Instructor
Geoff Mangum's PuttingZone http://puttingzone.com
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