[Yoda]

I find the pin orientation confusing - I assumed it was relative to your
frame of reference. The photo in TGM shows the theoretical pin in the left
shoulder parallel to the model's spine as she is standing vertically. It
seemed reasonable that the pin would remain parallel to the model's spine when
she assumed her stance and tilted forward at the hips. However, if the pin is
to remain perpendicular to the ground even when the address posture is taken,
the hinge pin shown in the picture would no longer be parallel to the spine
and would rotate to an oblique angle to the spine, in order to remain
perpendicular to the ground, as the model assumed her posture (picture not in
TGM). I can't get my mind around that.

Tough to imagine swinging around a pin vertical to the ground at a ball at
your feet and a hinge at your shoulder.


Sorry, just tough to get the image.

Again, the perpendicular positioning of the Hinge Pin to one of the three
Basic Planes of Motion is completely independent of any spine angle or body
posture. If, as you suggest, the model bends over more, the Pin doesn't
'bend' with her. It remains perpendicular to the horizontal plane. If it
helps, you might want to pretend like she had an operation and had her old
posture Hinge Pin removed and reinserted into the new.