applied the concept of double sampling (DS)
plans to suggest a DS X chart, where the out-of-control decision
at the combined-sample-stage is based on the information from
both samples. The attractiveness of the DS X chart is rooted in its
remarkably improved effectiveness in process monitoring without
increasing the sample size, while still maintaining the simplicity in computing the X chart’s statistics stated that when the incoming quality is either
very excellent or very poor, the DS X chart is attractive in requiring
a lower total sample size and thus, saving costs. This is because the
process is either declared to be in-control or out-of-control according
to the decision made at the first sample.