The Hanna Instruments Waterproof Salinity Tester comes armed with a state-of-the-art dual pin graphite EC probe to ensure the utmost accuracy when testing the salinity of your aquarium. The results of said test will be displayed immediately on a bright LCD screen in three different scientific units, those being either parts per thousand (ppt), Practical Salinity Units (PSU) and specific gravity (S.G.) based on your needs. This unit also comes stocked with 4 35.00(ppt) salinity calibration solutions to more accurately gauge and test the content of your water. Despite its small size and stature, the Marine Salinity Tester was designed with a durable casing to withstand any of the bumps, drops and splashes that happen around aquariums. The salinity tester features a battery that provides up to 100 hours of continuous use so that it is ready whenever you are. It's a fully loaded, industrial strength salinity tester that fits in your back pocket.