Constructed from an aluminium body and ABS rubber, the salinity refractometer is lightweight and extremely durable and comes with a hard plastic case, mini screwdriver, dropper and cleaning cloth. ATC FUNCTION: The salinometer has automatic temperature compensation to give you accurate readings every time. Simple to use: After calibration, place 2-3 drops of sample solution on the prism and hold it up to the light for an accurate reading.The Aqua Refractometer is an ideal replacement for a salinometer or an expensive digital salinometer. VERSATILE USE: The refractometer is designed for use in aquariums, marine monitoring, agriculture and educational purposes. It helps you monitor seawater concentration easily. Dual Scale: The Seawater Refractometer measures Specific Gravity (D20/20) 1,000-1,070 and 0-100‰, giving results in two different units in a single test.