The Refractometer is a well-established instrument used for measuring the water level of liquids. It measures the refractive index of the liquid, which changes according to the moisture content. In laboratory medicine, a refractometer is used to measure the total plasma protein in a blood sample and urine specific gravity in a urine sample. In drug diagnostics, a refractometer is used to measure the specific gravity of human urine. A refractometer is a simple instrument used for measuring concentrations of aqueous solutions. It requires only a few drops of liquid, and is used throughout the food, agricultural, chemical, and manufacturing industries.