= Goniometer
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A <goniometer> measures <angles> by comparing the orientations of a sample, beam or viewing arm. An optical implementation can rotate a specimen and detector about a common center, measuring the directions of reflected, refracted or diffracted <light>.
For a prism experiment, a collimated input and a viewing telescope determine the angle through which the beam is deviated as the prism rotates. For a reflection experiment, the incident and viewing directions define the scattering geometry. Accurate centering matters: an off-center sample can move out of the measured beam as the arm rotates, changing signal strength for reasons unrelated to angular response.
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