Overview for CUSUM chart

Use CUSUM Chart to detect small shifts in your process. The CUSUM chart plots the cumulative sums (CUSUMs) of the deviations of each sample value from the target value. Because the CUSUM chart is cumulative, even minor drifting in the process mean will cause steadily increasing (or decreasing) cumulative deviation values. The observations can be individual measurements or subgroup means.

For example, a manufacturer of centrifuge rotors wants to monitor the deviations from the target diameter of all rotors produced during a week. The diameters must be close to the target because even small shifts cause problems.

The points appear to vary randomly around the center line and are within the control limits, with the exception of one point. No trends or patterns are shown. The variability in the rotor diameter appears to be stable, but the out-of-control point should be investigated.

Where to find this control chart

To create a CUSUM chart, choose Stat > Control Charts > Time-Weighted Charts > CUSUM.

When to use an alternate control chart

  • If you do not want to detect small shifts in a process, use a variables chart for subgroups, such as Xbar-R Chart, or an variables chart for individuals, such as I-MR Chart.

  • If you want to detect small shifts in a process but want to use a more traditional control chart, use an EWMA Chart.
  • If your data are counts of defectives or defects, use an attribute control chart, such as P Chart or U Chart.