This paper presents a methodology for providing traceability to OCT measurements linked to Length SI unit. The link to primary length standard is provided by an interference microscope (IM). The chosen transfer standard was a step height gauge block. The results for IM and OCT showed good agreement for step height standards, such that the OCT will be able to perform reliable measurements of complex surface topographies and to ensure traceability to the length scale. The main uncertainty components were evaluated for the OCT system. In addition, OCT also was used for measuring a surface roughness standard -a depth standard -in order to test this methodology for round groove profiles. Results were found to be in good agreement with the calibration certificate.

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Main text A regional key comparison on calibration of a line scale, APMP.L-K7 was conducted. KRISS acted as the pilot laboratory, and a total of 15 National Metrology Institutes, (10 from APMP, 3 from EURAMET, 1 from SIM, and 1 from AFRIMETS) have participated in this comparison, where a 500 mm line scale made of low thermal expansion material was circulated during the period from April 2015 to December 2016. This document presents the approved report of the results of this comparison. 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 https://www.bipm.org/kcdb/. 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).

This supplementary comparison concerns the calibration of gauge blocks by mechanical comparison, which is a technique of paramount importance as it is at the highest level in the traceability chain of length for most countries of the American Continent. This comparison is designed to support the submitted CMC claims of these countries.The measurand is the central length of several gauge blocks as defined in ISO 3650 and the circulated gauge blocks were used for two comparisons carried out in two stages: the first stage, SIM.L-K1:2007, Calibration of gauge blocks by optical interferometry (2007–2010); the gauge blocks were also measured by mechanical comparison for those NMI also participating in SIM.L-S6:2007; the second stage, SIM.L-S6:2007, Calibration of gauge blocks by mechanical comparison (2010–2011) for the participants that measured only by mechanical comparison.In this second comparison there were 16 participants, 14 from the Americas, and 2 invited NMIs from other regions. The circulation in the second stage had 10 participants. 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).