The unit of volume is not an SI unit, but it is acceptable for use in International Systems of Units. Initially, the liter was defined as the volume of 1 kg of water (3rd CGPM, 1901). Then, it was accepted as the equivalent of 1 decimetre cube (12th CGPM, 1964). Later on, it was decided that the sign for litre would be "l" or "L” (16th CGPM, 1979). Traceability of volume measurements is disseminated by the Volume - Density Laboratory using the primary level standards based on the gravimetric measurement method using single-channel piston operated pipettes-burettes, glassware volumetric instruments and metal volume vessels. The unit used for density is the in international system of units SI, defined as the ratio of a substance’s mass to its volume; kg/m³. Traceability for hydrometers is provided using primary level laboratory standards based on the Cuckow method.
Viscosity is defined as the resistance of fluids against flow. This physical property can be divided into two major parts: dynamic viscosity and kinematic viscosity. The Viscosity Laboratory provides traceability to values that correspond to the kinematic and dynamic viscosity values of twice distilled water at normal atmospheric pressure (0.101325 MPa) with a density of 0.99820 g/cm³ at 20 ° C. The internationally accepted viscosity values of water are published in ISO/TR 3666:1998. Reference Ubbelohde viscometers are used to transfer traceability to secondary level laboratories.