Viscosimeter An instrument for measuring the viscosity of fluids (liquids and gases). Viscosity is the physical quantity that represents the internal friction inside the fluid when the fluid is flowing. It is the ability of the fluid to resist deformation and is an important indicator used to identify certain finished products or semi-finished products. The viscosity varies from fluid to fluid and varies with temperature. There are three types of capillary viscometers, rotary viscometers and falling ball viscometers.