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Recently, a scientific comparison of flatness measuring instruments at European National Metrology Institutes (NMIs) was performed in the framework of EURAMET. The specimen was a well-polished optical surface with a maximum measurement aperture of 150 mm in diameter. Here, we present an evaluation concept, which allows the determination of a mean flatness map taking into account different lateral resolutions of the instruments and different orientations of the specimen during measurement. We found that all measurements are in agreement with the mean flatness map within the uncertainty intervals stated by the participants. The aim of this scientific comparison is to specify an appropriate operation and evaluation procedure for future comparisons.

A trans-national optical fiber time transfer link, based on the White Rabbit Precision Time Protocol has between established between the UTC timescale realizations of the Belgian Metrology Service (SMD) in Brussels, Belgium and the ESTEC Radio Navigation Laboratory in Noordwijk, The Netherlands. The link consists of a single fiber covering a span of approximately 260 km. For verification, the optical fiber time transfer is compared with GPS-based common view time transfer. The results of the two techniques agree well within the combined uncertainties. The estimated uncertainty for the optical fiber time transfer is 0.2 ns.