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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.

This paper reports the fourth set of results of a series of grouped laser comparisons from national laboratories undertaken by the Bureau International des Poids et Mesures (BIPM) at the request of the Comite Consultatif pour la Definition du Metre (CCDM; now the Consultative Committee for Length, CCL) during the period July 1993 to September 1995. The results of this comparison, involving eleven lasers from eight countries and the BIPM, again meet the goals set by the CCDM in 1992 and adopted by the Comite International des Poids et Mesures (CIPM) the same year. The standard uncertainty of the frequency of the He-Ne laser stabilized on the saturated absorption of 127I2 at λ ≈ 633 nm is reduced to a level of 12 kHz (2.5 parts in 1011) when the lasers compared meet the recommended values of the parameters. The lasers were first compared with the BIPM4 laser with the parameters set to the values normally used in each laboratory; using the BIPM4 laser as a reference the results ranged from-15.4 kHz to 36.8 kHz. After checking and readjusting the values of all the parameters, the range was reduced to-8.6 kHz to 14.0 kHz. Under the latter conditions, the average frequency difference of the group of lasers, with respect to the BIPM4 laser, was 2.7 kHz with a standard uncertainty (1 σ) of 8.1 kHz. The best relative frequency stabilities, with Allan standard deviations of about 5.5 parts in 1012 and 4.6 parts in 1013, were observed with sampling times of 1 s and 100 s, respectively.

The key comparison EURAMET.L-K1.2011 on gauge blocks was carried out in the framework of a EURAMET project starting in 2012 and ending in 2015. It involved the participation of 24 National Metrology Institutes from Europe and Egypt, respectively. 38 gauge blocks of steel and ceramic with nominal central lengths between 0.5 mm and 500 mm were circulated. The comparison was conducted in two loops with two sets of artifacts. A statistical technique for linking the reference values was applied. As a consequence the reference value of one loop is influenced by the measurements of the other loop although they did not even see the artifacts of the others. This influence comes solely from three "linking laboratories" which measure both sets of artifacts. In total there were 44 results were not fully consistent with the reference values. This represents 10% of the full set of 420 results which is a considerable high number. At least 12 of them are clearly outliers where the participants have been informed by the pilot as soon as possible. The comparison results help to support the calibration and measurement capabilities (CMCs) of the laboratories involved in the CIPM MRA. Main text To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/. The final report has been peer-reviewed and approved for publication by the CCL, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).