To assign process variable levels
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1    In the Create Mixture Design dialog box, click Process Vars.

2    Under Low, click in the process variable row to which you would like to assign values and enter any value. Use the arrow key to move to High and enter a value. If you use numeric levels, the value you enter in High must be larger than the value you enter in Low.

3    Repeat step 2 to assign levels for other process variables. Click OK.

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To change the process variable levels after you have created the design, use Stat > DOE > Modify Design.