A Comparative Method Of Checking Angles On Glass Samples

An optical method of checking angles on glass samples is described. The method is comparative: the reference is a polished sample, the angle of which has been measured on a precision goniometer. It has the advantage that angles with either polished or fine ground surfaces can be measured since use is made of reflections off the faces of the angle at close to grazing incidence. Angles with fine ground surfaces can be checked to 5 seconds of arc and with polished surfaces to 2 seconds of arc.