Use R Chart to monitor the variation (range) of your process when you have continuous data and subgroup sizes of 8 or less. Use this control chart to 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.
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.