To add process variables to a design
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1    In the Create Mixture Design dialog box, click Process Vars.

2    Under Process Variables, choose Number, then choose a value from 1 to 7.

3    From Type of design, choose a full or fractional factorial design. The available designs depend on the number of process variables chosen.

4    If you like, you can select the fraction number you want to use. By default, Minitab uses the principal fraction. See Choosing a fraction.

5    If you like, you can name the process variables and set the process variable levels.

6    Click OK.