Our supplier had provided there test results. Using Mini tab I calculated the Cpk's. Of course with hardness testing the only specification limit is a minimum. But the Cpk's are .96, .7 and .710. that seems extremely low. These are 3 measurements taken on different portions of the part. If we tried asking the supplier to improve the consistency of the hardness would it increase the hardness overall to get a better Cpk? Notes: yes the distribution is normal for all 3 measurements. The Cpk was done on 95 measurements over time.