The viscosity is a quantity describing the flow behaviour of fluids. It is a measure for the inner friction.
The realization of the viscosity is carried out per definitionem with regard to the value of viscosity of water at standard conditions (20 °C, 101325 Pa). Liquid viscosimeters can be compared with this reference. Additionally, the BEV has several capillary viscosimeters calibrated by the Physikalisch-Technischen Bundesanstalt (PTB, Germany).