In the Process Capability launch window, the options in this section enable you to assign historically accepted values of the standard deviation to variables in the Y, Process list.
1. Select a variable or variables in the Y, Process list.
2. Enter a value next to Set Historical Sigma.
3. Select Use Historical Sigma to assign that value to the selected variables.
The specified value appears in parentheses in the expression “&Sigma()” to the right of the variable names in the Y, Process list.
Note: If you set a historical sigma, then subgroup assignments for the selected process variable are no longer relevant and are removed.