[rwh]

Neil - you state that one institutes a 1/4 turn of the clubface by the end-takeaway and after that there is only rotation.

Neil referenced the position where the club is parallel to the ground (where it is also parallel to the plane line). This is Section 5 of the 12 Sections in Chapter 8.

How does one turn the clubface 1/4 turn if not by rotation?

The clubface can turn by swivel (forearm rotation), only; right forearm takeaway, only; body rotation (pivot), only; or, combinations thereof.

What is the difference in rotary technique employed in turning the clubface 1/4 turn during the start-up swivel versus the technique of rotation of the left arm/forearm that occurs throughout the remainder of the backstroke?

None, if we restrict the discussion to opeining the clubface by rotating the forearms.

The left hand/leading edge of the clubface begin at approximately 90° to the plane line at address. At the top, the left hand/leading edge are laying on the plane angle (in Mr. Appleby's case, the Turned Shoulder Plane). The forearms need not rotate any more than to accomplish this.

Once you reach Station 5, the forearms have rotated enough to allow the left wrist/leading edge of the clubface to open about 90° such that they are now more or less parallel to the plane line. From Station 5 to the Top (8-6), the right forearm is pulling the club back, up and in (on-plane) with the result that the left hand will lay on the plane angle without much more, if any, forearm rotatation. In my own case, I have almost no further forearm rotation. Do some very slow motion backswings watching only your forearms and I think you find this is the case. The combination of pivot and right forearm movement is post-Station 5 "rotation" to which Neil referred.