Hydrostatic weighing at KRISS

To minimize the density correction of the transfer liquid in hydrostatic weighing, a new hydrostatic weighing machine with a single-step immersion pan was constructed. With this machine the volumes of two Zerodur® density-standard spheres (Z2, Z1), used as primary density standards at KRISS from 1992 to 2000, were measured against a silicon density-standard sphere that will be used as the new primary density standard. The relative measurement precision of the hydrostatic weighing was shown to be 7.7 × 10 −7 , and the expanded uncertainty of the volume measurement was found to be 2.6 × 10 −5 cm 3 for Z1 and Z2 with a confidence level of 95% and a coverage factor of 1.97, giving relative uncertainties of 6.7 × 10 −7 for Z2 and 7.9 × 10 −7 for Z1.