313964d8_Microscopy__Determinative_value
[Optical property] Optic sign [Measurement] Convention based on relative magnitudes of refractive indices. By comparison of values of refractive indices or by means of compensators. [Determinative value] 
Aid in the identification of crystals, minerals and fibers. For artificial fibers the more easily determined sign of elongation is the same as the optic sign.
Microscopy
Determinative value