Does anyone have any positive or negative comments about the Itech clear hockey shields (full face, not just covering the eyes)? I'm looking at the Concept II, as well as the X200
You don't. That's part of the problem with being someone stupid enough to ruin a good vehicle by screwing up the ground clearance..
It is not clear to me whether you are working in visible region or in microwave region. Your question is clear to me how we can know whether the two surfaces are exactly parallel or not . I shall concentrate on that. If you make that surface part of Michelson's interferometer and use extended source (I think laser is not extended source of light) of visible light and obtain frings when there is no path difference between the two coherent beams, we get rings only when both beams are reflected from parallel faces otherwise we get straight fringes. This fact can be utilized to solve your problem.
