Digital refractometers measure the refractive index of a gel, liquid or solid sample to in order to determine the sample’s concentration. Since more concentrated samples bend light at a larger angle, digital refractometers operate by illuminating the sample against a prism and digitally measuring the angle of refracted light with photodiode detectors. Digital refractometers are used to measure a variety of substances, from the concentration of sugar in grape juice to the purity of solvents, and are widely employed in production and quality control applications in the food, chemicals and pharmaceutical industries. Digital refractometers may be designed for manual, semi-automatic or fully automatic sample reading. Compared to an analog instrument, a digital refractometer offers quick and extensive selection between measurement units and easily exports results. The upper and lower reading limits vary significantly between digital refractometer models. Temperature-controlled digital refractometers, for ranges up to 10 to 120°C, provide better accuracy by compensating for the changes in a sample’s refractive index caused by heat or cold. Handheld digital refractometers offer convenience but may be less accurate and require larger sample sizes compared to desktop instruments. Some digital refractometer models are designed for specific applications with more limited capabilities but optimized performance.