Cusum Chart

Definition of Cusum Chart:

A type of control chart (cumulative sum control chart). It is used to detect small changes between 0-0.5 sigma.

For larger shifts (0.5-2.5), Shewart-type charts are just as good and easier to use. Cusum charts plot the cumulative sum of the deviations between each data point (a sample average) and a reference value, T.

Unlike other control charts, one studying a cusum chart will be concerned with the slope of the plotted line, not just the distance between plotted points and the centerline. Critical limits for a cusum chart are not fixed or parallel. And a mask in the shape of a V is usually laid over the chart with the origin over the last plotted point.

Previous points covered by the mask indicate the process has shifted.

So, who uses these types of charts? Typically chemical industries.

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