How to Use: 1: Wipe the gemstones to be tested and the refractometer table, and apply 1 to 2 drops of refraction oil evenly on the surfaces of the prism. 2: Put the gemstones to be tested on the platform, let the gemstones completely cover the surfaces of the prism, and ensure that the refracting oil is in full contact with the gemstones. 3: Press the tail of the flashlight to turn on the light source. Specification: Item Type: Portable Gemstones Refractometer Material: Glass, ABS Product size:Approx. 128 x 60 x 32mm / 5.0 x 2.4 x 1.3in Measuring Range: 1.30 to 1.81 Minimum Division Value: 0.01 Liquid: Refractive Oil (Shipped with Liquid) Flashlight Battery: 1 x 1.5V AA Battery (Shipped Without Battery) Weight: Approx. 590g / 20.8oz Package List: 1 x Portable Gemstones Refractometer 1 x Flashlight 1 x Refractive Oil 1 x Box 1 x User Manual Note: 1.The refractive index of gemstones is a very important optical parameter. The gloss of the gemstones can be determined by this parameter. Since different gemstones have a fixed refractive index, all kinds of gems can be determined according to the refractive index. Birefringence can also be measured. This parameter can be used to determine whether a gemstones is uniaxial or biaxial.2.Shipped with liquid, shipped without battery.