Face centred cube design

Face-centred cubical design a = 1, which is useful if the region of interest is a cube. This approach will place the values in the centre of the plane defined by the factorial experiment. 

The three-factor central composite may be represented as a cube, with a centre point, experiments at each vertex and at the ends of axes radiating out from the centre through the middle of each face. The vertices will be designated as +1 or -1 for each factor. It is suggested that six runs be made at the centre, This design can be represented as indicated below the diagram,... 

An example of an experimental design for a three-component mixture, where each component is varied independently, is based around a cubic design. This cube has points at each corner (8 of them) at the centre of each face (6) and in the centre (1). Each point corresponds to a unique combination of concentrations. The point in the middle is the specified concentration, all the others contain one or more components present in either higher or lower than average concentrations. If H is higher than the specified concentration, L is lower and M the average ( correct concentration), then the other 14 points can be described as follows ... 

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