The Single Plane Golf Swing Arm position represents the plane at address where the golf club starts and Impacts on the same plane.This video explains the two crucial alignments of the Single Plane swing including the lead arm and club (Rod) and the trail arm and club (Single Plane) alignment.
Like striking a ball on the ground with a stick, the Two-Lines represent the alignment of the club and the arm creating the Single Plane where the trail arm and lead arm lines make it easier to reproduce the moment of impact – making the swing easier to repeat.