This refractometer is design according to the principle that different concentrations liquid have different refractive index ,with quick and accurate characteristics. Salinity refractometer is widely used for aquarium, marine monitoring, fish tank, seafood water tank, salty pools& spas and used for saline solution tester for education purpose or agricultural.Features: The salinity tester needs testing sample less than a traditional hydrometer, just 2 to 3 drops and wait for few seconds, you will get accurate readings. Saltwater refractometer Specific Gravity (D 20/20) and parts per thousand and replaces your poor quality and difficult to read hydrometer.Salt meter with dual scale: 0~100?(1?=1PPT=1000ppm, PPT means"parts per thousand", specific gravity range 1.000 to 1.070 Automatic compensation temperature (ATC) function makes the refractometer more accuracy, shifts in ambient temperature within 50?-86? won?t effect the readings. Easy to calibrate and easy to operate, optic salt refractometer no batteries required, more cheap than a digital refractometer. Handheld salt water tester is made of non-staining, non-corrosive aluminum and ABS plastic, lightweight and easy to carry, durable to use for long time.Method of Using: 1.Calibration: just 2-3 drops of distilled water or fresh water, using mini screwdriver to calibrate. Through the eyepiece to check the blue line is on zero. 2. After calibration, place a 2-3 drops of test sample onto the Clean main prism 3. Close the daylight plate and hold it under a light source, then check the reading. 4. After used, use the cleaning cloth to wipe the prism and storage.Package Included: 1 x Refractometer 1 x Plastic pipette 1 x Mini Screw Driver 1 x Cleaning Cloth(Random color) 1 x Plastic BoxNOTE: Accurate measurement depends on careful calibration