To implement statistical quality control, we first need to understand the causes of variation
in our process. We aim to identify and remove what is known as special cause variation and to
keep common cause variation, to a minimum level. The next step is to establish that our process
can meet the customer's specification, and that our product will continue to meet that specification
during its design lifetime. Statistical quality control charts are used to monitor the process
and so provide early warning of any new sources of special cause variation and any increase in the
common cause variation.
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