Modify Design - Add Axial Points
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Stat > DOE > Modify Design > choose Add axial points > Specify

You can add axial points to a two-level factorial design to "build" it up to a central composite design. The position of the axial points in a central composite design is denoted by a. The value of a, along with the number of center points, determines whether a design can be orthogonally blocked and is rotatable. For a discussion of axial points and the value of a, see Changing the value of a for a central composite design.

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

Dialog box items

Value of Alpha

Default (rotatable if possible): Choose to have Minitab determine the value of alpha (a) based on the design you selected. The default value of a provides rotatability whenever possible.

Face centered: Choose to generate a face-centered design (a = 1).

Custom: Choose to specify the a value; then enter the desired value in coded units. A value less than 1 places the axial points inside the cube; a value greater than 1 places them outside the cube.

Add the following number of center points (to the axial block): Enter a number.