[Martee]

Do you think the term "plane shift" is apt when what most /all people do ( including Leadbetter - hence your X classification) is a "plane drift"?

Plane angle can readily be defined at 4 points in all swings.

1. Address

2. Left arm horizontal to ground

3. Top/end of backstroke

4. Impact

plus maybe Follow through/ both arms straight.

Most golfers ( I would argue all golfers) drift planes between these positions. During drift the butt/end of club rarely points at target line unless the drift happens rapidly around clubshaft horizontal ( and therefore ideally parallel to plane line).

Leadbetter people basically are double shifters - categorised by their address / impact location and top/end of backstroke positions. They may drift a bit more than others off TGM plane at left arm horizontal but 90 % of people drift not shift!

Why the left arm horizontal as a definition point?

If we are talking about the club being on plane, I would have expected the definition points, a more universal set, would be the club, not the left arm....