Gritomatic Goniometer

[Mike Brubacher]

All of this has piqued my curiosity. I'd be interested in learning how well these work and how much, if any, the bevel polish affects the user's ability to clearly identify the bevel angle. My question is based in this: The light emitted by a diode laser is "coherent" meaning that all the photons are at the same frequency. This is what gives laser light the ability to "hang together" and resist scattering through air as normal or incoherent light does. Once that coherent light strikes a  surface though, it diffuses or scatters commensurate with the roughness of the surface. Scattered light would manifest as reflected light producing a sort of blurry edge  making it difficult, I would think, to determine the precise bevel angle. Of course highly, polished bevels would reduce this occurrence but even glass mirrors of the highest quality do not provide perfect specular reflections. A high quality glass mirror might be 90% reflective. I have no good idea what a high quality polished metal surface might provide but I would guess - perhaps 40%? 

If anyone has experience with these devices I would be interested in learning how well defined they are and how the bevel size and polish affect the ability of the user to read the results accurately