Enter a historical proportion for Laney P' Chart

Stat > Control Charts > Attributes Charts > Laney P′ > P′ Chart Options > Parameters

Enter the historical value for the proportion that Minitab uses to calculate the center line and control limits. If you do not specify a parameter, Minitab estimates the proportion from the data. You can enter a single proportion for the entire chart, or you can enter a proportion for each stage.