Salinity Refractometer for Seawater and Marine Fishkeeping Aquarium 0-100 Ppt with Automatic Temperature Compensation Measure salt water or salinity of water, ideal for aquariums and marine monitoring. Measures on 2 scales, Specific Gravity (D 20/20) and parts per thousand. Features automatic temperature compensation. Comes with hard case, dropper, screwdriver, user manual and cleaning cloth. The main part is made of chromium, it's very durable.