An international comparison has been made of the frequencies of stabilized He-Ne lasers using intracavity saturated absorption of 127I2 at λ = 633 nm in Bratislava (Czechoslovakia).This comparison, organized by the CSMU (Bratislava), involved at the same time seven laboratories from five countries: the ASMW (German Democratic Republic), the CSMU (Bratislava, Czechoslovakia), the CSMU (Praha, Czechoslovakia), the CSAV (Brno, Czechoslovakia), the OMH (Hungary), the VNIIM (USSR) and the BIPM.The range of the frequency differences between all the lasers and the two BIPM travelling lasers was from - 15,9 kHz to 8,8 kHz, with a mean of Δf = - 3,3 kHz and an estimated standard deviation of 8,5 kHz (4,7 kHz corresponds to 1 part in 1011, in relative terms).Using the measurements carried out at the BIPM before and after this comparison between the travelling lasers BIPM4 and BIPM10 and the stationnary reference laser BIPM2, we can link our results to previous international comparisons involving the BIPM. Taking into account the values of these measurements, the mean frequency difference becomes: Δf = - [1,6 ± 8,2] kHz.

The results of the inter-RMO key comparison EUROMET.L-K5.2004 on the calibration of a step gauge are reported. Eighteen National Metrology Institutes and one Designated Institute from four different metrological regions all over the world participated in this comparison which lasted three years, from December 2004 to December 2007.A lack of stability was observed through the shifting of some of the inserted gauges. In order to save the comparison and get valuable and useful conclusions, it was agreed to exclude four gauges from calculation and assume that only seven gauges were reasonably stable so as to get the corresponding reference values. It was also agreed to divide the participants into two groups, analyze separately their results and, taking the pilot as the linking laboratory, refer the results to common reference values.The inverse-variance weighted mean was taken as reference value. Due to the significant instability of the step it was also considered an artefact uncertainty. The reported uncertainties ranged from 0.045 µm to 1.2 µm (k = 1). The uncertainty of the artefact ranged from 0.018 µm (for the 20 mm face) to 0.176 µm (for the 400 mm face).The compatibility of all participants for measuring step gauges was demonstrated with the only exception of a participant showing very high systematic (both positive and negative) errors. Five participants communicated higher uncertainties than the corresponding approved CMCs. A set of Recommendations and Actions were agreed therefore.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).

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).

Autocollimators are versatile optical devices for the contactless measurement of the tilt angles of reflecting surfaces. An international key comparison (KC) on autocollimator calibration, EURAMET.L-K3.2009, was initiated by the European Association of National Metrology Institutes (EURAMET) to provide information on the capabilities in this field. The Physikalisch-Technische Bundesanstalt (PTB) acted as the pilot laboratory, with a total of 25 international participants from EURAMET and from the Asia Pacific Metrology Programme (APMP) providing measurements. This KC was the first one to utilise a high-resolution electronic autocollimator as a standard. In contrast to KCs in angle metrology which usually involve the full plane angle, it focused on relatively small angular ranges (±10 arcsec and ±1000 arcsec) and step sizes (10 arcsec and 0.1 arcsec, respectively). This document represents the approved final report on the results of the KC. 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).

An international comparison of He-Ne/I 2 lasers at λ 633 nm between the CMI (Czech Republic), the OMH (Hungary) and the BEV (Austria) was performed at the CMI-LPM, Prague, in July 1997 as DUNAMET project D3. The frequencies of three national standards of length (lasers) were found to be in the range ± 7 kHz (1.5 parts in 10 11 ) and reproducibility of frequency differences between individual lasers during one week was better than ± 5 kHz (1 part in 10 11 ). The relative frequency stability, expressed as an Allan standard deviation, reached a minimum of 3 parts in 10 13 for an integration time of 10 000 s.