How do you adjust tonearm damping?

I have an SME 309 tonearem with the FDIV fluid damper. How do I know when the damping for my tonearm is correctly adjusted.?
I set mine so the paddle is just touching the fluid, but have a different arm......
On the Goldmund I do it by ear: When sssybilants become sybilants, the mids are open and the bottom is nice and tight, I'm satisfied.