[Daryl]

Look at the Illustration on the left. The hands stay under plane until they get the the end of the backstroke. Then, somehow, a miracle occurs and the Clubshaft, hands and right shoulder are against the same flat inclined plane. If the Hands and club-shaft switch planes during the backstroke, then how does that happen?

Look at the Illustration on the Right. Extensor Action Raises the Hands and Clubshaft to the TSP before the Backstroke is completed and allows the hands to sense the plane of the club-shaft. Both go to the end of the backstroke perfectly on-plane and ready for an on-plane down-stroke.

Zero shift is Zero shift. Both of the Illustrations above demonstrate a Single Plane Shift. But the one on the right is not as disruptive as the one on the left.

The illustration on the left show you to turn the shoulders and then lift the arms to the top of the swing. The one on the right shows you to lift the arms which then turns the shoulders to the top.

The illustration on the right shows a conscious effort to trace the plane-line all the way to the top of the swing.