Overview for S Chart

Use S Chart to monitor the variation (standard deviation) of your process when you have continuous data and subgroups sizes of 9 or more. Use this control chart to monitor process stability over time so that you can identify and correct instabilities in a process.

For example, a paint manufacturer wants to determine whether the filling process for cans of paints is stable. Operators collect subgroups of 10 cans every hour for 30 hours and use an S chart to monitor the variation of the filled paint cans.

The points vary randomly around the center line and are within the control limits. No trends or patterns are present. The variation of the weights of cans are stable across the 30 subgroups.

Where to find this control chart

To create an S chart, choose Stat > Control Charts > Variables Charts for Subgroups > S.

When to use an alternate control chart

  • For subgroups that have 2−8 observations, use R Chart.
  • If you do not have subgroups, use Moving Range Chart.
  • If your data are counts of defectives or defects, use an attribute control chart, such as P Chart or U Chart.