The argon pressure measured by a spinnig rotor gauge (MKS SRG-2), P
SRG, has been compared to the pressure measured by an ionization gauge, P
IG. The linearity of P
SRG as compared to P
IG was previausly observed between 10
-1 and 10
-4 Pa using the average value of the residual drag, P
OFS, by other authors. In the present study, the value of P
OFS has been newly determined using data obtained in the range above 2×10
-5 Pa, where the fluctuation of P
OFS becomes relatively small. P
OFS was determined such that the standard deviation of [Log (P
IG) -Sa⋅Log (P
SRG-P
OFS) -Log (Sb)] was minimized. Here, Sa and Sb are constants and nearly equal 1. The linearity was found to extend to a lower pressure region using the P
OFS obtained in present method, as opposed to that obtained by the conventional averaging method. It was found that the standard deviation of P
SRG at constant pressure was proportional to T
-2.5, where T is a sampling interval used with the SRG. This relation is valid up to 10
-6 Pa.
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