Hi SJ, I am new to six sigma, just posted my thouhgts on the this question, please provide your comments on the same:- A product or service that has a value of 9.999 will be termed good (in-spec) while a value of 10.001 will be termed as bad (defect). In reality, both these products will probably operate very similarly or will probably be indistinguishable by the customer. It is better to have our control limits fixed so that we may take an action when we are going beyond the control limit rather than taking a call on the spec limit as it may be a very thin line. Regards, LR