Dear SJ Sir, Though I agree with your point, I would like to emphasise that most of the organisations still work on specification limits. Only highly matured organisations are looking for targetting at center value or optimum value. In reality, when a product or service performance is approaching specification limits ( Either lower / upper or away from spec for one sided spec ), it indicates that is is almost nearing the deviation. In my opinion working with control limits (If possible) will be the better approach than working with specification limits. When a product or service performance deviates from control limits, we can initiate necessary corrective action to eliminate the assignable cause and bring back the performance to normal . In such cases the performance will never become defect as it will never cross specification limits. Please correct me if I am wrong. Regards KVS Suresh