Diameter determination of Avogadro sphere #1 and #2

In the scope of the new determination of Avogadro's constant, NA, the spheres interferometer of PTB was developed to measure the volume of the Avogadro sphere. The interferometer is based on spherical reference plates and spherical beams of rays. This allows not only one diameter in the center to be measured, but a big amount of diameter measurements available in a 60deg field of view. With all orientations of this 60deg cone a sphere is characterized by 500 000 diameter values. Avogadro sphere #1 of PTB and Avogadro sphere #2 of IMGC have been measured in 40 different orientations, so that fundamental knowledge of the spheres can be given. The additional information of surface topography leads to better understanding of uncertainty