A cusum chart is more efficient for detecting small shifts in the process mean, in particular, shifts of 0.5 to 2 standard deviations from the target mean (refer to Montgomery 1996). Lucas (1976) ...

Figure 12.5: One-Sided Cusum Chart with Decision Interval The cusum plotted at HOUR=t is S t = max(0,S t-1 +(z t-k)) where S 0 =0, and z t is the standardized deviation of the t th measurement from ...