This part of ISO 9110 establishes procedures for measuring the average steady-state pressure in a hydraulic fluid power conduit. It is applicable to the measurement of average steady-state pressure in closed conduits with inside diameters greater than 3 mm, transmitting hydraulic fluid power with average fluid velocities less than 25 m/s and average steady-state static pressures less than 70 MPa (700 bar). It is not applicable to sensors which are flush mounted with, or are an integral part of, the closed fluid conduit wall. It provides the formulae for estimating the total uncertainty in a given pressure measurement.