Diameter determination of Avogadro Spheres #1 and #2

For the redetermination of Avogadro´s constant, N_A, the spheres interferometer of Physikalisch-Technische Bundesanstalt (PTB) was used to measure the volume of two of the Avogadro spheres. With spherical reference plates and spherical beams of rays not only one diameter in the center is measured, but also covering a 60° field of view a topography with a large number of diameter measurements. About 40 different orientations of this spherical caps result in 500 000 diameter values for the sphere. Avogadro sphere #1 of PTB, Germany, and Avogadro sphere #2 of IMGC, Italy, have been measured with different setups. For the last measurement the calculation of the radius is based on a new algorithm taking the spatial distribution of the measured data into account. As the spheres have different diameters the absolute density of both spheres were calculated with the aid of the mass measurement. The agreement is within 4·10^-8.