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 very 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 very 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 aqueous solutions 1. water -Less than 0.5 2.Brackish water -0.5 to 30 3.Saline water (Seawater)-30 to 50 4.Brine- more than 50 (Salinity 36 means, that there are 36 grams of salt in 1 liter aqueous solution.) Measurement: The liquid measurement is very easy. Place a few drops of the liquid on the optical part of the refractometer, cover the prism (the liquid will spread more easily over the prism), look throught the eyepiece against the light (focus, if necessary) and you will be able to read the result value on the scale. reference temperature 20 Celsius - automatic temperature compensation (compensation range 0 ~ 30 Celsius) focus possibility length ~ 195 mm quality technical design colour:black Material:Aluminum alloy + plastic Package Contents: 1 * firm plastic case 1 * refractometer 1 * cleaning cloth 1 * suction tube 1 * screw driver 1 * operating instructions Only the above package content, other products are not included. Note: Light and different displays may cause the color of the item in the picture a little different from the real thing. The measurement allowed error is +/- 1-3cm.