The following diagrams show the eccentric mounting technique
The (grey) faceplate has four holes in a square formation, offset to one corner
The multicoloured "blank" has four fixing holes, giving four mounting positions
As the blank is repositioned, it can rotate about four different centres
And the four centres are the same even when the blank is flipped over
Here is what the faceplate looks like, note the four fixing holes in a square. The larger holes were used for counterweight mounting