n An instrument used to measure a spectrophotometric curve at various angles of incidence and reflectance. The angles of incidence and reflectance may be changed. On goniochromatic samples, the results obtained are dependent on the angles of incidence and reflectance, and on samples exhibiting specular reflectance (glossy materials), the results are also dependent on the total subtended angle of viewing relative to the specular angle. (Willard HH, Merritt LL, Dean JA (1974) Instrumental methods of analysis. D. Van Nostrand, New York).