The problem with all this is that the shaft (or more exactly the sweetspot line) doesn't move on the same plane in the BS and DS in any effective golf swing I've ever seen. In fact on the BS, the shaft traces out a curved surface. A look at the latest edition of Golf Magazine's sequence of Ken Perry will show you that even in the some DOWNSWINGS, the shaft traces a curved surface.
Better to put lasers out the butt of the shaft and pointing from #3 PP to the plane line just in front of the leading edge of the clubface. This, at least, allows a diferent "plane" for the BS than the DS.
Your observation would seem to be accurate if the reference point is the PGA Tour. However, the variation selected for component 6/7 in 12-1-0 and 12-2-0 and the accompanying photos in 10-13-B,D conveys to me the intent of a single plane. This is an area I continue to struggle with. I had though the answer might be with the sweet spot but that is not clear. I will continue to lister!
Threaded Mode
