In the appraisal standard, data items such as density, refractive index, birefringence and absorption spectrum of various jewelry and jade varieties often have a data range, such as ruby, refractive index:1.762 ~1.770 (-0.009, +0.005). 1.762 ~ 1.770 is the theoretical value of ruby, and its refractive index may change in the range of (-0.009, +0.005) due to the different composition and origin of ruby.

The refractive index depends not only on the substance, but also on the wavelength of light. If there is no specified wavelength, it is generally considered as the refractive index corresponding to the yellow light of sodium lamp (wavelength is 589nm).

In a few cases, the measured data slightly exceeds the listed data range and cannot be completely denied. We must make a comprehensive judgment based on other data and various observations in order to reach an accurate conclusion.