[Yoda]

Being "on plane" is a basic concept that I thought I understood but now I am confused.

What plane can apply to the whole swing from start to finish?

Any of the five defined Basic Plane Angles (10-6-A/B/C/D/E) executed with Zero Shift (10-7-A).

The Zero Shift Variation can be executed with the Shoulder Planes (10-6-B/C/D) only with an Address Postion that features a "steeper than normal Elbow Plane", a "reaching out of the Arms"'; and a Zero #3 Accumulator (7-23 / First six editions).