Xbar-S chart

An Xbar-S chart is a combination of control charts used to monitor the process variability (as the standard deviation) 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.
• S chart
  An S-chart is a type of control chart used to monitor the process variability (as the standard deviation) when measuring subgroups (n ≥ 5) at regular intervals from a process.