4. Derivative instruments

4.1 Pressure balance and liquid column manometer

Fundamental type instruments can be used as derivative instruments by calibrating them by direct comparison with a pressure standard. This is the most commonly used approach. Two calibration methods are available:

• a "global" method in which the equivalent pressure, measured by the instrument in a given configuration and under defined reference conditions, is measured using the standard;

• a method allowing a priori a better uncertainty, where the instrument parameters are calculated from the pressure measured by the standard.