Hand starts and 45 degrees and ends at 45 degrees, s the elbow comes to centerline. The energy must come from the foot to the hand. This Is much more difficult then it seems. The tendency for me was to bend the wrist independent from the arm and to move the arm out with no regard for the line. I found it very helpful to stand on a tiled floor which allowed me to better concentrate on the line. By doing this I found that the line allowed me to better keep arm on the line and my wrist better alignment with the rest of the arm.