The Model 290 pycnometers are used to determine the density of paints and other liquid or paste-like products. The density (r) of a substance is the quotient of its mass (m) and its volume (V). The reference temperature for the density of paints is 20 °C, unless otherwise agreed. The density at 20 °C is designated as r20. The pycnometers used to determine the density are filled with the liquid or paste to be tested. The density is calculated from the weight difference between the filled and empty pycnometer and the known filling volume.