Comparison of mean diameters of silicon spheres measured with both spherical fizeau-interferometers of the PTB

The sphere interferometer 2 of the PTB was set up to undercut the measurement uncertainty already reached by the sphere interferometer 1 of the PTB. This was necessary for being able to meet the conditions of the CCM for a redefinition of the SI-unit kilogram where the sphere interferometers are used to measure the volume of the Avogadro spheres. This paper summarizes the comparison measurements between both interferometers and their results.