Use Xbar-R Chart to monitor the mean and variation of a 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 manufacturing engineer wants to determine whether the production process for a new plastic product is in control. Operators sample 5 units every hour for 20 hours and assess the strength of the plastic.
Where to find this control chart
To create an Xbar-R chart, choose Stat > Control Charts > Variables Charts for Subgroups > Xbar-R.
When to use an alternate control chart
For subgroups that have 9 or more observations, use Xbar-S Chart.
If there is a consistent source of variation within the subgroups, use I-MR-R/S