With single wrist action the right forearm wedge (which from address is resting on the (let’s say turned shoulder) plane) will remain on plane as the club is moved up to the position where it is parallel to the plane line – a sort of windscreen wiper motion of the whole right arm flying wedge. The right elbow will be ‘up the plane’ from the right hand.
With standard wrist action the club and right hand will stay on plane as the club is taken back but the right elbow will immediately begin working inside the plane, so that at the point where the club is parallel to the plane line the right forearm [wedge] will also be parallel to the ground.