The I-MR-R/S Chart is located on the left side of the Capability Sixpack - Between/Within.

Use the I-MR-R/S chart to determine whether the process is in control. The process should be in control before you begin to assess capability. If the process is not in control then the process capability indices will be inaccurate.

Whether Minitab displays an R chart or an S chart depends on the size of the subgroups. If more than 50% of the subgroups are the same size, then the most common subgroup size determines the chart. Otherwise, the largest subgroup size determines the chart. If the subgroup size is 8 or less, Minitab displays an R chart. If the subgroup size is 9 or more, Minitab displays an S chart.

The I-MR-R/S chart consists of the following:

·    The Individuals (I) chart plots the subgroup means. Use the I chart to determine whether there is a shift in the process average.

·    The moving range (MR) chart plots moving ranges for consecutive subgroup means, Use the MR chart to assess whether the process variation from subgroup to subgroup (between subgroups) is in control.

·    The R chart plots the subgroup ranges. Use the R chart to determine whether the variation within subgroups is in control.

·    The S chart plots the subgroup standard deviations. Use the S chart to determine whether the variation within subgroups is in control.

Examine the I-MR-R/S chart for points located beyond the red control limits. Points located beyond the control limit signal that the process is out of control. Capability analyses should only be conducted when the process is in control.

For the coating data, the subgroup size is 5, so an I-MR-R chart is displayed. No points are located beyond the control limits, therefore the process is in control, and further capability analyses can be conducted.