Gadget Hero's Salinity Refractometer that is used to measure the salinity levels of saltwater aquariums and the worlds oceans. Calibrate with either distilled water or a 35ppt Salinity standard. Wipe off the saltwater after each use. This unit comes with Automatic Temperature Compensation or "ATC". This feature allows you to get a reading outdoors when the temp is between 50'F-86" (10'C-30'C). If you test outside of temp range your readings will become gradually more and more inaccurate. For best results, test indoors. No batteries necessary as you only need strong light - daylight (sunny or cloudy) or a lamp/flashlight. Details : This optical refractometer (salinity meter) has scales in the range of 0 - 100 ppt(0 - 10 %). The reading resolution is 1 ppt. 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 selected aqueous solutions Fresh water ------50 ppt Example:Salinity 36 ppt 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. General technical parameters · reference temperature 20 C · ATC - automatic temperature compensation (compensation range 0 ~ 30 C) · focus possibility · length ~ 175 mm · quality technical design Content and equipment · a firm plastic case · a refractometer · a cleaning cloth · a suction tube · a screw driver · operating instructions