[alojoo]

Does the left arm rotate on the backswing? If it does how much?

I think he means rotate as to turn, a straight rod rotating around the AXIS of its extension.

With 10-18-A the left wrist, arm(from left shoulder pin to the hands) and club are turned or rotated ClockWise.

This is done while mantaining the clubhead all the time in its angular motion, all the time in its single plane, that is the sweetspot plane.

Turning of the left wrist is executed until getting the left wristcock plane of motion into the sweetspot plane. In other words, this turning is executed until
the entire left arm, the clubshaft and the back of the left hand are positioned against the same flat plane, the sweetspot plane. So the left flying wedge plane matches/gets into the sweetspot plane.

So then, after this the left wrist now would be TURNED, after turning. And hands, clubshaft are now in the sweetspot plane, they were not (before) in the sweetspot plane (because clubshaft rotates around the sweetspot not viceversa) while the whole time the clubhead was and will be in the intented sweetspot plane.

Clubshaft and hands have come to be in the sweetspot plane, they were not before in this plane because of nº3 accumulator angle. But always the clubhead remained in the sweetspot plane.

Don't complicate it I'm still incubating some concepts, so all this is with zero shift, 10-7-A when I refer to a single/unique plane although I feel Homer Kelley is more referreing in section 10-6 about clubhead planes rather than clubshaft control, because clubshaft motion is three dimensional until it gets (and hands get in, left flying wedge) gets into and match/lie the sweetspot plane intended for the stroke purposes. While clubhead travel/trajectory is 2 dimensional, always the motion of the clubhead is along the sweetspot plane, a flat surface circular, 2 dimmensional motion.

Now the machine is ready to begin the downstroke.

People are free to say if this comment is right or wrong. If it is right then an important part of the golfing machine concepts have been cleared out.