"This little machine will be the best teacher you ever had. Just listen to what it is telling you to do with that student in front of you. One of the club delivery numbers will be way off right out the gate in 95% of the lessons you will ever give."
Bet on it.
"Think of club delivery like this: The sweetspot is traveling on a arc, on a plane in the lower portion of the swing. That plane has a certain inclination, and the whole plane is aligned horizontally out in space. While the club is traveling on that arc, on that plane, on that certain inclination, the ball gets struck in a three-quarter of an inch slightly straightened portion of the arc. If that portion of arc is on the way-down toward the bottom of the arc, the resulting club path will be to the right of the horizontal alignment of the plane. If contact occurs on the portion of arc is on the way up from the bottom of the arc, the resulting club path will be to the left of the horizontal alignment of the plane. Only when the middle of the three-quarter of an inch impact interval is at the very bottom of the arc, is the club path also aligned at the same location as the horizontal alignment of the plane. The inclination of the nearly dead-straight middle of the three-quater of an inch impact interval to the ground is called the angle of attack. The directional vector of the instantaneous path portion of the three-quarter of an inch impact interval that occurs at maximum compression, is the bottom of another plane called the D-Plane—the plane the ball flies on. That plane's other vector is the clubface normal, the perpendicular to the portion of the clubface that contacts the ball. On an iron that perpendicular vector is pointing out in space as a lie angle tool attached anywhere to the clubface would. But on a club with bulge and roll, like some hybrids and nearly all woods, the clubface normal is perpendicular to the exact place on the clubface that ball contacts. Rightward toward the toe, leftward in the heel, high and low, when struck high and low on the face and all the obvious combinations. On a shot where the clubhead's center of gravity is precisely aligned to the instantaneous path and the impact point of the face, an in effect so-called sweetspot strike, the ball will travel on this D-Plane, starting about 85% toward the clubface normal vector on a shot where the two vectors are relative close together, and toward 70% toward the clubface normal when the two vectors are further apart. The ball will fly on this plane until wind or gravity take it off of it's course.
And then there is off-center strikes....." —Brian Manzella
