Where L is the width of the control limits. is σZi . It should be noted that the term : obtains to unity as i increases.
2.1.3. Cumulative sum. The chart was proposed by Page17; it is memory chart that uses both present and past information to detect small and moderate shifts in the mean of a process, which is now one of the most popular charts used to monitor processes. For this chart, two statistics Cþi and C i are computed and plotted on against an interval limit H. The statistics are defined as