Unilateral Tolerance Capability - Shaft Runout - Which capability index to use?

Does anyone have some ideas on which capability index (s) should be used when monitoring runout on a shaft with a unilateral?

Al:
I have run into the same question. I think using (mean+3s)divided by the allowable tolerance is a valid way of expressing the capability of such a process. But I am not sure if this a valid approach.

Originally posted by Al Dyer:
Does anyone have some ideas on which capability index (s) should be used when monitoring runout on a shaft with a unilateral?

ASD...

Hi Al,
I tend to use PpU / CpU ;
(Upper spec limit - double bar X) divided by 3 sigma to give capability of making parts within maximum tolerance.

Does anybody know if there is a "target figure" for this index, e.g. Cpk >1.33 / Ppk >1.67 ?