This model is Gemological refractometer. It can be used for measuring Refractive index of Gemstone or Ore. The index of double refraction can be also measured. Through the parameter you can judge whether a gem is uniaxial or biaxial photopositive or photonegative.
For more convenient using, this item have built-in LED light source, the LED can at least offer 10000hours working! And also, the special design offers other way to get the light source if the built-in light source can't work, there is a light entrance in the back side and the filter for light source also built-in. A small torch as outside light source also included without any extra cost!

Specifications:
Measuring Range: 1.30 - 1.81 RI
Minimum Graduation: (RI) 0.01 RI
Illumination: Internal Light Source with momentary/power switch
Dimension: 125mm x 70mm x 4mm
Scale Division : 0.01 nD
Weight: 0.6 kg
Filter: Polarizing filter
Power:4.5V button type batteries(3pcs)