Professional ATC Sea Water Salinity Refractometer w/ 35ppt Calibration Fluid for Aquarium, Hydrometer, 0-100ppt & 1.000-1.070 Salinity Specific Gravity Hard Case unit WITH 35ppt Salinity Calibration Standard - 3.6ml Vial Resale Quality - 50% heavier than the soft case cheap units Dual Salinity Scale - 0-100ppt & 1.000-1070 Salinity SG Perfect for testing salinity