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Not sure if this is the right forum, but here goes anyway. I have been asked to provide a tolerance for a manufacturing process. Yes, I know that the tolerance is the VOC, but in this instance the customer has asked for our advice on setting a tolerance, as we know from experience that the tolerance the customer is asking for is not acheivable. The customer is ameniable to changing the tolerance, provided it is not too outrageous. What they mean by that is open for discussion. The process yields a CP value of 1.725 and a standard deviation of 0.0887. The tolerance at the moment is ±.2mm. Now, just taking 3xstd deviation gives me ±.27mm, but I don't think that is the right thing to do. Is there a formula I can use to calculate the tolerance?