I'm still exploring the 'instantaneous' skate force that AS is trying to compensate. Due to modulation, skate force can instantaneously be much larger than a typically AS setting, and point the 'wrong way' to be compensated by AS for some of the time !
IMO the best that AS can do is compensate the average
skate force, which has only limited value. It also helps extreme instantaneous trackability in a relatively small way, sort of in a 'straw and camel's back' improvement situation.
So IMO AS is not critical, but might as well optimise it if the mechanism is there.
Average skate force arises from average friction acting along a line different from the tonearm axis. It can be possible to measure the average friction, using a simple method, most recently posted here http://www.vinylengine.com/phpBB2/viewt ... g&start=82
[BTW, ignore the correction posted afterwards, the original was correct !]
Once one obtains a measured value for friction coefficient Cf, the average skate force, SF, is approx
SF = VTF * Cf * sin(tracking offset angle) [gf]
In principle, the AS should be set to equal SF.
Cf is typically in the range 0.22 - 0.55, say 0.35 typ. Tracking offset angle say 20 degrees. VTF typically 1.5 gf. Then optimal AS might typically be 0.18gf.
HOWEVER Cf varies from disc to disc, across the surface, and dependant on modulation level at which it is measured. So I wouldn't get too hung up about exact AS setting.
Using blank (ungrooved) vinyl often gives a way too high value for Cf, as it depends on the base of the stylus digging into the vinyl. It's so different from the normal mode of stylus/vinyl contact as to be generally useless, IMO.
Bottom line IMO : Don't get too hung up about AS setting. It's only an average in a wildly fluctuating dynamic situation. Even zero is a respectable number.