This report describes a CCM key comparison of hydraulic pressure standards of nine national metrology institutes that was carried out in the period from November 2002 to June 2004 in order to determine their degrees of equivalence in the range 10 MPa to 100 MPa of the gauge pressure. The pilot laboratory was PTB. The primary pressure standards were pressure balances of different design equipped with piston-cylinder assemblies operated in free-deformation, controlled-clearance or re-entrant operation mode. The transfer standard was a pressure balance equipped with a piston-cylinder assembly and a mass set. The pressure-dependent effective areas of the transfer standard at specified pressures were reported by the participants and led to the reference values calculated as medians. All participants' results agree with the reference values and with each other within the expanded uncertainties calculated with a coverage factor 2, most of them even within their standard uncertainties. In addition, the results were analysed in terms of the zero-pressure effective area and the pressure distortion coefficient. Also for them agreement within expanded uncertainties (k = 2) is observed. The results of the comparison demonstrate equivalence of the laboratory standards and support their measurement capability statements.

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The final report has been peer-reviewed and approved for publication by the CCM, according to the provisions of the Mutual Recognition Arrangement (MRA).