Overview for R Chart

Use an R Chart to monitor the variation (range) of your process when you have continuous data in subgroups of sizes of 8 or less. R charts monitor process stability over time so that you can identify and correct instabilities in a process.
For example, a plastics manufacturer wants to determine whether the variation in the production process for a new product is stable. Analysts collect subgroups of 5 products every hour for 20 hours and assess the strength of the plastic.

The points vary randomly around the center line and are within the control limits. No trends or patterns are present. The variability in the strength of the plastic product is stable across the 20 subgroups.

Where to find this control chart

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

When to use an alternate control chart

  • For subgroups that have 9 or more observations, use S 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.