Wulsy you asked "The question is how instant is instant and how much of the bottom of the swing arc is actually measured.?"
I think you might check Brian's comments from after the Anti Summit as to when the important stuff in impact occurs or ought to be measured, because Trackman is a little silent about that. Brian was saying you would take the D Plane numbers, iirc, at the point the ball is maximally compressed. Also somethign like the club is in contact with the ball for, what 3/4 inch?, and the clubface closed 1 degree or so while the club was on the ball.
I think you might check Brian's comments from after the Anti Summit as to when the important stuff in impact occurs or ought to be measured, because Trackman is a little silent about that. Brian was saying you would take the D Plane numbers, iirc, at the point the ball is maximally compressed. Also somethign like the club is in contact with the ball for, what 3/4 inch?, and the clubface closed 1 degree or so while the club was on the ball.
