The Aqua Medic Refractometer is a precision optical instrument used to determine the salt concentration in saltwater aquaria. Its exact value can be determined in seconds and can be read either as absolute salt concentration (, ppt) or as specific density. When a beam of light enters the refractometer it is bent or refracted by the water in the test panel. This refraction is proportional to the salinity of the sample and can be directly read by viewing the internal scale. The integrated LED illumination provides good readability even in poor lighting conditions. The temperature compensation ensures accurate measurement results, even with different water temperatures.Included in shipment: refractometer, a pipette for the water sample, a screw driver for calibration, desalinated water, LED display and a strong plastic box.