Xbar-R chart

An Xbar-R chart is a combination of control charts used to monitor the process variability (as the range) and average (as the mean) when measuring subgroups at regular intervals from a process.

• Xbar chart
  An Xbar-chart is a type of control chart used to monitor the process mean when measuring subgroups at regular intervals from a process.
• R chart
  An R-chart is a type of control chart used to monitor the process variability (as the range) when measuring small subgroups (n ≤ 10) at regular intervals from a process.