Roundness profiles are compared which were obtained from measurements carried out at five national metrology laboratories. The object used for this comparison was a zirconium-oxide sphere with a profile containing higher harmonics and a total roundness deviation of about 42 nm. The measurement results were obtained using different and independent measuring instruments and different evaluation methods for spindle error separation. The number of data points used ranged from 50 to 4096. Before the analysis, the profiles were transformed to a common digital data format containing 1024 points and a correlation analysis was carried out to determine a common zero position for the profiles. In the analysis, standard deviations and maximum deviations were calculated from point-by-point differences of the profiles with reference to one another or to the average profile. Fourier analysis was used to select a spectral area for an analysis at the edge of the significance limit. The comparison shows that each participating laboratory is able to measure a roundness profile with a standard deviation in each data point of less than 2 nm.
The results obtained by five laboratories in the determination from dimensional measurements of the effective areas of two gas-operated 10 cm2 piston-cylinder assemblies are presented. These measurements were carried out as phase A1 of a key comparison in the pressure range 0.05 MPa to 1 MPa under the auspices of the Consultative Committee for Mass and Related Quantities (CCM) of the Comité International des Poids et Mesures. The participants performed diameter, straightness and roundness measurements on each piston and cylinder bore and calculated the effective area of each piston-cylinder assembly using their own methods. The differences between diameters determined by the institutes are systematic and often greater than the uncertainties claimed by the participants. Nevertheless, all calculated effective areas agree with the reference values determined within the expanded uncertainties with a coverage factor 2, most of them even within their standard uncertainties. The choice of calculation method seems to be less important than the dimensional data themselves. The effective areas determined from the dimensional measurements are compared with those obtained in cross-float experiments with national pressure standards, in a comparison referred to as phase A2 and reported in a separate paper.
The density p of two silicon crystals has been determined by precision hydrostatic weighing, based on very accurate solid density standards (SDS's). Densities of additional crystals were gained from density differences measured by the temperature-of-f1oatation method. The molar mass M of the crystals was determined by comparing the isotopic abundances against the known abundances of the National Bureau of Standards (NBS) reference material SRM 990 using activation analysis and mass spectroscopy. Combining the measured values for M and p leads to M / p = (12.058 822 ± 0.000 013) cnr' / mol. With the known volume of the unit cell the following value for the Avogadro constant was calculated: N A = (6.022 137 ± 0.000 007) x 10 23 mol-I.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.