To add axial points
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1    Choose Stat > DOE > Modify Design.

2    Choose Add axial points and click Specify.

3    Do one of the following:

·    To have Minitab assign a value to a, choose Default.

·    To set a equal to 1, choose Face Centered. When a = 1, the axial points are placed on the "cube" portion of the design. This is an appropriate choice when the "cube" points of the design are at the operational limits.

·    Choose Custom and enter a positive number in the box. A value less than 1 places the axial points inside the "cube" portion of the design; a value greater than 1 places the axial points outside the "cube."

4    If you want to add center points to the axial block, enter a number in Add the following number of center points (in the axial block). Click OK.

Note

If you a building up a factorial design into a central composite design and would like to consider the properties of orthogonal blocking and rotatability, use the table in Summary of central composite designs for guidance on choosing a and the number of center points to add.

This option is not available for split-plot designs or designs with text factors.