In Reply to Parent Post by malak
first i try to solve it by varible control chart to find x bar averge
and find upper specification limit
but what another analysis can complet this case?
Step back a moment before charting the data further. Recognize that the data are being influenced by the settings of the operator.
I'd suggest looking up and reviewing Dr. Deming's "Funnel Experiment". This sounds like a classic example of tampering with the product setting.
I'll make the following prediction - you may find if you think through the logic that the operator would be better off NOT TOUCHING THE SETTING rather than trying to keep chasing the latest results.