[O.B.Left]

The left wrist is ideally Flat Level and Vertical but Flat and Vertical are relative terms. Relative to grip type. If you during your backswing Arch your left wrist to achieve a literally flat left wrist you have broken your Left Arm Flying Wedge Alugnment.

The left hand hangs naturally in what we would call a slightly turned manner although there is no turn involved. If there is a nutral this is it. The elbow is turned too a's it's aligned to your mouth naturally. Not perpendicular to a golfers square plane line.

If you arch your left wrist to achieve a literally flat left hand at top you are not Flat in tgm terms.

The face being square to the left arm idea at Top is also Relative. Relative to Grip Rotation. For a ball played back of Low Point by a golfer who Rotates his grip, the face will appear more closed so to speak at top or in follow through. As it should.

Literaly flat or parrallel to the left arm at top is common and logical but only correct under specific conditions. A week left hand grip rolled literally level at fix and no grip rotAtion a's in a ball played at low point.

See the photo in the book that accompanies flat level and vertical ........ It's grometrically flat not literally flat.

It's a Mellon scratcher but hopefully a useful one. To get it wrong is to compromise a lot of your alignments take Hinge Action for instance.