A new control region can be defined for the process shift by selecting the Change Limits button in the Analysis Options dialog. This opens the Stepped Control Limits dialog, where multiple (stepped) regions (and how limits are calculated within each) can be defined.
For example, to fix control limits based on an initial study of 30 or more subgroups, define the Default for all groups region with limits calculated using the second radio button selection: Groups from 1 to 30.
For this example, select the Add button, then add a region starting with Group 31 (with no ending group). Each region will use the first radio button option for calculating the limits: All plotted groups in region.
