Augmentation of a simplex design adds interior points to allow the detection of lack of fit. The center point and check blends are added to the design. Check blends are half way between the center point and each vertex.
To evaluate the lack of fit, an estimate of pure error is necessary. This estimate of pure error comes from replication of several design points. The program uses the number of components plus one, to a limit of 5, to determine the number of replicate points. The points with the highest leverages are replicated.