Manning - An early attempt to solve the symmetry problem proposed a rotor with a circular staircase cut into it. Because of the symmetry of the staircase, the retardation would be constant across the aperture. There are no advantages to this design. Disadvantages include extreme susceptibility to misalignment, the estimated US$50,000 to 100,000 (in 1996 dollars) to build a prototype, and possibly dispersion from the small facets. As it turns out, exotic surfaces are not required to solve the symmetry mismatch.