Measure salt water or salinity of water, perfect for aquariums and marine monitoring.Measures on 2 scales, Specific Gravity (D 20/20) and parts per thousand.Features automatic temperature compensation.it's durable.This optical refractometer (salinity meter) has scales in the range of 0 - 100 (0 - 10 %). The reading resolution is 1 . It is designed for the measurement of seawater (marine aquaria) or low concentrated salt solutions.The second scale is for reading of the salt solution density in range 1.000 to 1.070 g/cm3 (resolution 0.001 g/cm3).The usual salinity of the solutions 1. water -Less than 0.5 2.Brackish water -0.5 to 30 3.Saline water (Seawater)-30 to 50 4.- more than 50 (Salinity 36 means, that there are 36 grams of salt in 1 liter solution.)Measurement:The liquid measurement is easy. Place a few of the liquid on the optical part of the refractometer, cover the prism (the liquid will spread more over the prism), look throught the eyepiece against the light (focus, if necessary)and you will be to read the value on the scale. reference temperature 20 CelsiusATC - automatic temperature compensation (compensation range 0 ~ 30 Celsius) focus possibility length ~ 195 mm quality technical design colour:blackMaterial:Aluminum alloy + plasticPackage Contents:1 * plastic case 1 * refractometer 1 * cleaning cloth 1 * suction tube 1 * screw driver 1 * operating instructions