Cumulative Sum Control Charts
Detect Small Shifts in the Process Mean
CUSUM charts show cumulative sums of subgroup or individual measurements from a target value. CUSUM charts can help you decide whether a process is in a state of statistical control by detecting small, sustained shifts in the process mean. In comparison, Shewhart charts can detect sudden and large changes in measurement, such as a two or three sigma shift, but they are ineffective at spotting smaller changes, such as a one sigma shift.
Figure 5.1 Example of a CUSUM Chart