These include (\(p\),\(V\), \(T\)) measurements, saturated density measurements, and any other measurements which give information on the (\(p\),\(V\), \(T\)) surface of a fluid.
Source: PAC, 1981, 53, 1805. (Assignment and Presentation of Uncertainties of the Numerical Results of Thermodynamic Measurements) on page 1818 [Terms] [Paper]