Modify the control limits for I-MR-R/S Chart

Stat > Control Charts > Variables Charts for Subgroups > I-MR-R/S (Between/Within) > I-MR-R/S Options > Limits

Display additional σ limits at

In These multiples of the standard deviation, enter one or more values to display additional standard deviation lines on your control chart.

For example, you can display additional limits at ±1 and ±2 standard deviations. Values that you enter affect only the line position on the control chart, not the test results.
Default 3 sigma limits
Additional sigma limits at 1 and 2 standard deviations

Place bounds on control limits

You can specify a lower bound and an upper bound for the control limits. If the calculated control limit is farther from the center line than the value that you specify, Minitab displays the bound instead of the control limit. Minitab labels the lower bound as LB and the upper bound as UB.

Note

Upper bounds and lower bounds do not affect the calculations for any of the tests for special causes.

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