Serenity Seawater Refractometer Correct salinity is crucial for the survival and health of your fish and corals. This high-quality refractometer is extremely accurate and easy to use and calibrate. This also features ATC (automatic temperature compensation). Comes with Carry case, Pipette and Calibration Screwdriver   Calibration is simply done with a few drops of a known salinity reference like the Accurasea  (Sold separate) Range  from 0-100 ppt and 1.000 to 1.070 specific gravity