Johny B Good wrote:

Since the drag from the stylus is pretty closely aligned to the
offset angle the drag force is trying to pull the stylus towards the
spindle and is only restrained from doing so by the resultant increase
of force on the inner groove wall. The best analogy I can think of is
that of keeping a horse drawn barge away from the bank the towpath is
on by judicious use of the tiller to compensate the shorward component
in the towing force vector provided by the horse.

I'm still struggling with all this.

Still:

* the horse (tonearm pivot) stands firmly stationary by the side of the
canal

* the horse is connected to the barge (stylus) not with a rope, but a
rigid bar, that means horse and barge must always face the same
direction

* the rapidly-flowing canal (the vinyl groove) tugs at the barge as it
goes by

* because the horse is offset from the direction of the water's tug, the
whole assembly of horse, bar and barge wants to rotate around the horse,
towards the bank

I think I understand that, but it must be more complicated.

For example, when the needle is in the middle of the side (assuming
that's where the tonearm is parallel to the tangent of the groove) that
would be like having the horse directly upstream of the barge, not to
one side.

And, either side of that middle, the force on the tonearm must always be
towards the middle of the side, suggesting you'd need positive bias
adjustment for the first half and negative bias for the second.

Daniele