Abstract. This report describes the key comparison APMP.M.P-K1.c.1 among the three national metrology institutes, Center for Measurement Standards-ITRI (CMS-ITRI, Chinese Taipei), SPRING Singapore and National Institute of Metrology (NIMT) in the pressure range from 0.4 MPa to 4.0 MPa in gas media and gauge mode executed during the period April 2003 to April 2004. This comparison was conducted by CMS-ITRI and was based on the calibration procedure of APMP Pneumatic Pressure Comparison APMP.M.P-K1.c. We intended to link to the key Comparison APMP.M.P-K1.c via the results of SPRING Singapore. All three participating institutes used pneumatic piston gauges as their pressure standards. The Ruska 2465 gas-operated piston-cylinder assembly V-1215 used as a transfer standard offered by CMS-ITRI was calibrated three times by the pilot institute during the comparison period and showed that it was very stable after evaluation. The comparison was conducted on the basis of cross-float experiments to determine the effective area of the transfer standard from the national standards of three institutes. The mean value of the results obtained by all participating institutes measuring the same quantity from 0.4 MPa to 4.0 MPa in gas media and gauge mode lay within their expanded uncertainty with a confidence level of 95%. Linking key comparison APMP.M.P-K1.c to key comparison APMP.M.P-K1.c.1 at two nominal pressures near 1 MPa and 4 MPa was established.

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