The refractometer is an instrument that measures the concentration of a specific substance in a liquid solution. It uses the principle of refraction, which describes how light bends as it passes through a material. The sample is placed on a plate and then held up to the light to view the scale inside the meter. The reading scale is usually calibrated to determine the concentration of a specific substance. There is a wide variety of refractometers for different materials such as soap oil, antifreeze liquids, battery fluids, salinity, honey, alcohol, wine, Urea AdBlue, sugars, coffee, etc.