07-04-2018, 07:44 AM
The scale is a semicircle centered at the knife edge. Correct angle markings require only that the scale compass 180 degrees, is divided into equal segments, and is centered around zero.
As the reflected spots are the result of twice the edge angle (angle of incidence + angle of reflection,) compassing 180 degrees translates into scale markings which compass 90 degrees: -45 degrees at the left end of the scale, and +45 degrees at the right end of the scale.
As the reflected spots are the result of twice the edge angle (angle of incidence + angle of reflection,) compassing 180 degrees translates into scale markings which compass 90 degrees: -45 degrees at the left end of the scale, and +45 degrees at the right end of the scale.