Modern accurate methods for monitoring the concentration in solutions and measuring the density of liquid samples are impossible without digital instruments. Previously, in laboratories and industrial enterprises, sets of hydrometers were used for these purposes. The use of hydrometers has significant drawbacks: a large measurement error, the glass case is susceptible to mechanical damage and does not meet the safety requirements of food and chemical enterprises. Also, hydrometers must be selected for different densities of liquids. A digital laboratory density meter solves these problems and guarantees high measurement accuracy and safety when working with flammable and toxic substances. For operational measurement of the concentration of solutions in production or in the field, digital refractometers are successfully used. Refractometers allow you to find out the Brix of sugar syrup or sugar-containing products such as honey. In industry, refractometers are used to determine the concentration of urea, brines, glycols, and battery fluid. An automatic refractometer recalculates the refractive indices corrected for temperature and gives a compensated result.