The ability to measure step height and to calibrate step height artefacts is of vital interest in nanometrology. On that score the WGDM7 decided in 1998 to include measurements of step heights in a series of comparisons on the field of nanometrology.The comparison about step height (NANO2) started in September 2000 with the Physikalisch-Technische Bundesanstalt (PTB) as pilot laboratory. Fourteen national metrology institutes worldwide participated in this comparison. A set of five step height standards in the range from 7 nm to 800 nm was used for the comparison. The lateral size of the structures of the step height standards was chosen so that the height could be measured by different types of instruments, for example, interference microscopes, stylus instruments and scanning probe microscopes (SPM). The reference values were calculated as the weighted mean of all measurements that fulfilled the En < 1 criteria.Most of the results were in good agreement with the reference values. It is noticeable that the results obtained by different types of instruments are quite compatible. Also this comparison is the first comprehensive test of the reliability of SPM and their suitability for traceable measurements of step heights. Further it was shown that today step heights on samples can be measured with uncertainties in the sub-nanometre range. Differences in the calculation of the uncertainty depend on the types of instruments and on the users. For each class of instrument, e.g. SPM, it would be meaningful to homogenise these models. Hence the results of this comparison are of great importance in many respects.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 Mutual Recognition Arrangement (MRA).

This second Northern European comparison between seven lasers exhibits closer results than the ® rst comparison. A standard uncertainty of 5 kHz was obtained against 15 kHz in 1990, while the frequency average of the group of lasers was about the same with 3,9 kHz, using the BIPM4 laser as reference. A large frequency difference on a laser observed during the ® rst com parison was again observed; partial explanations of the origin of this differenc e were found. This differenc e has been excluded from the calculation of the average. Typical frequency stabiliti es using Allan standard deviations of about 1,6 10 ±11 and 1,7 10 ±12 were observed on 1 s and 100 s sampling tim es, respectively. * are the characteristics of the M 1 m irror located on th e iodin e cell sid e of the lasers. ** are th e characteristics of th e M 2 m irror located on the gain tube sid e of the lasers. * T he m odulatio n w idth is alw ays give n in M H z peak-to -peak. ** E xterna l powe r of the laser.

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 Comité Consultatif pour la Définition du Mètre (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 Comité 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 127 I 2 at λ 633 nm is reduced to a level of 12 kHz (2.5 parts in 10 11 ) 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 ) of 8.1 kHz. The best relative frequency stabilities, with Allan standard deviations of about 5.5 parts in 10 12 and 4.6 parts in 10 13 , were observed with sampling times of 1 s and 100 s, respectively.

Results of the Stage One portion of the Inter-American System of Metrology (SIM) regional international comparison of gauge block calibration by optical interferometry are presented. In this measurement round-robin, short gauge blocks, six made of steel and six made of tungsten carbide, in the range of nominal length from 2 mm to 100 mm, were calibrated by five national metrology institutes (NMIs) of the SIM region, and one NMI from EUROMET. By employing the technique of optical interferometry, each of the laboratories establishes a direct link to their national primary standard of length through the calibrated laser wavelengths. Results of central length calibration are presented and discussed with regard to vacuum wavelength correction for refractive index of air, phase-change on re.ection and wringing effects. Measurement uncertainty evaluation is also discussed.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 (MRA).

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).