The oscillating U-tube densitometer method is a technique to determine the density of liquids and gases based on an electronic measurement of the frequency of oscillation, from which the density value is calculated.Density meters work by measuring the oscillation of a glass tube containing the sample. Specific gravity and refraction index can be measured. They are used in many industries such as: oil, chemical, food and beverage industries for quality control and research and development. Density meters are especially useful when working with viscous liquids or difficult gases.Also called Hydrometer
ρ= A∙τ² - B
A hydrometer is an instrument used to measure the specific gravity (or relative density) of liquids; that is, the ratio of the density of the liquid to the density of water.