Evaluation of the conductance of the I.N.RI.M. continuous expansion system D2

The results of the NPL–I.N.RI.M. bilateral comparison (Euromet Project 855) in the pressure range from Pa to Pa showed that I.N.RI.M. data were not equivalent to NPL data. Afterwards, I.N.RI.M. started a series of investigations about its primary vacuum standard, the continuous expansion system D2, which confirmed that the reason of the disagreement between I.N.RI.M. and NPL was due to an incorrect estimate of the conductance between the calibration and the pumping chamber of the system D2. In present report are detailed: - the implementation of a correction for non-molecular regime; - the conductance measurements of a capillary and the calibration of a spinning rotor gauge, carried out at PTB and I.N.RI.M.; - the method adopted for the new evaluation of the conductance of the system D2