Aqua Medic Salinity Refractometer with ATCHaving an accurate measure of an aquariums salinity or specific gravity is essential to every marine enthusiast. Our Refractometer is the fastest, easiest, and most accurate way to know. Simply add a drop of your system water to the lens, close the cover, and look through the adjustable focus eye-piece to read the clearly marked value across a simple scale. Far more accurate than dip and read style hydrometers and easier to use than floating hydrometers, our Refractometer is a must have for every marine aquarium hobbyist. This high-quality measurement device reads in both salinity and specific gravity values that are temperature compensated and can be easily calibrated with a drop of freshwater. Each Reefractometer comes in a padded case, complete with a fine-adjustment tool, sample pipette, and full instructions.