Slipper setting

[grindog]

Hi all, what is the right slipper adjustment. I am unsure exactly how much slip these should give as i come from touring cars and adjustment trackside is virtually impossible as it requires the curing of threadlock?
I always give it a guess and it is either no slip what so ever or its slipping its bag off. I have set the diffs a quarter turn back from fully tight and when holding the car, the slipper does slip before the diff but it is this adjustment that i am stuck on. How easily should the slipper spin when doing this test?

thanks, john