Primary vacuum systems of the Electrotechnical Laboratory (ETL) and th
e Istituto di Metrologia ''G. Colonnetti'' (IMGC) were compared in the
pressure range 10(-4) Pa to 10 Pa by using spinning rotors as transfe
r gauges. Several rotors were calibrated at both laboratories in an ar
gon atmosphere. The results obtained are in good agreement and are wit
hin the uncertainty values of both the laboratories.