BIPM Key Comparison Research Articles

AFRIMETS supplementary comparison on calibration of caliper

Main textNational Metrology Institutes from 12 African countries, namely Egypt, Morocco, Ghana, Nigeria, Ethiopia, Kenya, Tanzania, Zambia, Zimbabwe, Botswana, Mauritius and South Africa have participated in an international supplementary comparison on the calibration of caliper.This comparison was a part of larger supplementary comparison between 13 African countries for the calibration of hand measuring instruments. This larger comparison which was carried out during the period between December 2019 - December 2022 has been piloted by NIS, Egypt and has been registered in BIPM-KCDB database on December 2019. The artifacts have been prepared by NIS, Egypt and measured before sent to circulate between all participant countries in round-robin scheme and returned back again for NIS, Egypt where a final measurement was made for stability check.The main purpose of these comparisons is to support submission of CMCs for calibration of hand length measuring instruments in BIPM-KCDB.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).

AFRIMETS supplementary comparison on calibration of feeler gauges

Main textNational Metrology Institutes from 8 African countries, namely Egypt, Morocco, Nigeria, Tanzania, Zambia, Zimbabwe, Botswana, and South Africa have participated in an international supplementary comparison on the calibration of feeler gauges.This comparison was a part of larger supplementary comparison between 13 African countries for the calibration of hand measuring instruments. This larger comparison which was carried out during the period between December 2019 - December 2022 has been piloted by NIS, Egypt and has been registered in BIPM-KCDB database on December 2019. The artifacts have been prepared by NIS, Egypt and measured before sent to circulate between all participant countries in round-robin scheme and returned back again for NIS, Egypt where a final measurement was made for stability check.The main purpose of these comparisons is to support submission of CMCs for calibration of hand length measuring instruments in BIPM-KCDB.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).

AFRIMETS supplementary comparison on calibration of dial gauge

Main textNational Metrology Institutes from 11 African countries, namely Egypt, Morocco, Nigeria, Ethiopia, Kenya, Tanzania, Zambia, Zimbabwe, Botswana, Mauritius and South Africa have participated in an international supplementary comparison on the calibration of Dial Indicators.This comparison was a part of larger supplementary comparison between 13 African countries for the calibration of hand measuring instruments. This larger comparison which was carried out during the period between December 2019 - December 2022 has been piloted by NIS, Egypt and has been registered in BIPM-KCDB database on December 2019. The artifacts have been prepared by NIS, Egypt and measured before sent to circulate between all participant countries in round-robin scheme and returned back again for NIS, Egypt where a final measurement was made for stability check.The main purpose of these comparisons is to support submission of CMCs for calibration of hand length measuring instruments in BIPM-KCDB.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).

AFRIMETS supplementary comparison on pin gauges

Main textNational Metrology Institutes from 6 African countries, namely Egypt, Nigeria, Zambia, Zimbabwe, Botswana, and Mauritius have participated in an international supplementary comparison on the calibration of pin gauges.This comparison was a part of larger supplementary comparison between 13 African countries for the calibration of hand measuring instruments. This larger comparison which was carried out during the period between December 2019 - December 2022 has been piloted by NIS, Egypt and has been registered in BIPM-KCDB database on December 2019. The artifacts have been prepared by NIS, Egypt and measured before sent to circulate between all participant countries in round-robin scheme and returned back again for NIS, Egypt where a final measurement is made for stability check.The main purpose of these comparisons is to support submission of CMCs for calibration of hand length measuring instruments in BIPM-KCDB.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).

AFRIMETS supplementary comparison on calibration of setting rods

Main textNational Metrology Institutes from 8 African countries, namely Egypt, Nigeria, Kenya, Tanzania, Zambia, Zimbabwe, Botswana, and Mauritius have participated in an international supplementary comparison on the calibration of setting rods.This comparison was a part of larger supplementary comparison between 13 African countries for the calibration of hand measuring instruments. This larger comparison which was carried out during the period between December 2019 - December 2022 has been piloted by NIS, Egypt and has been registered in BIPM-KCDB database on December 2019. The artifacts have been prepared by NIS, Egypt and measured before sent to circulate between all participant countries in round-robin scheme and returned back again for NIS, Egypt where a final measurement was made for stability check.The main purpose of these comparisons is to support submission of CMCs for calibration of hand length measuring instruments in BIPM-KCDB.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).

Report on key comparison AFRIMETS.AUV.V-K5 and linking to CCAUV.V-K5

Main textFollowing the completion of the fifth CIPM key comparison (KC) in the area of vibration concerning sinusoidal acceleration, participating Regional Metrology Organizations (RMOs) have the responsibility to disseminate the Key Comparison Reference Values (KCRV) to non-participating National Metrology Institutes (NMIs), thereby establishing a traceable link between NMIs participating in regional comparisons and the KCRVs. The comparison results reported here have that objective. The comparison was piloted by AFRIMETS with participants from three NMIs, situated in two RMOs, namely SIM and APMP.The respective Degrees of Equivalence, linked to the KCRVs, are reported. The final report has been peer-reviewed and approved for publication by the CCAUV, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).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 CCAUV, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

CIPM MRA support for hydrogen metrology – A case study

The CIPM Mutual Recognition Arrangement (CIPMMRA) provides one of the most profound frameworks for internationally recognized metrological traceability to the international system of units (SI). National Metrology Institutes demonstrate the international equivalence of their measurement standards and the calibration and measurement certificates they issue through the CIPMMRA. CIPMMRA activities comprise the organization and evaluation of key and supplementary comparisons (KCs/SCs) and the declaration of calibration and measurement capabilities (CMCs) in the BIPM key comparison database (KCDB). In this contribution we showcase up-to-date CIPMMRA activities that could be used in support of hydrogen as a future option for the diversification of energy sources. Relevant metrology areas are chemistry and biology, thermometry, mass, and length. There are already 3 KCs in progress within the CIPMMRA that are directly related to the hydrogen topic and a number of earlier KCs/SCs on other relavant quantities. Todate, the KCDB contains CMCs published by National Metrology Institutes which are dealing exactly with hydrogen as the analyte or which relate to measurement capabilities that are relevant in the context of hydrogen as future energy source.

Bilateral comparison of 1.018 V and 10 V standards between INRIM (Italy) and the BIPM, November to December 2023 (part of the ongoing BIPM key comparison BIPM.EM-K11.a and b)

Main textAs part of the ongoing BIPM key comparison BIPM.EM-K11.a and b, a comparison of the 1.018 V and 10 V voltage reference standards of the BIPM and the INRIM (Italy), from November to December 2023. Two BIPM Zener diode-based travelling standards (Fluke 732B), BIPM_7 (Z7) and BIPM_9 (Z9), were transported by freight to the INRIM and back to the BIPM. In order to keep the Zeners powered during their transportation phase, two additional external batteries were connected in parallel to the internal battery. At the INRIM and the BIPM, the reference standard for DC voltage is a Programmable Josephson Voltage Standard (PJVS). The output electromotive force (EMF) of each travelling standard was measured by direct comparison with the primary standard. The final result of the comparison is presented as the difference between the values assigned to DC voltage standards by the INRIM, at the level of 1.018 V and 10 V, at the INRIM, UINRIM, and those assigned by the BIPM, at the BIPM, UBIPM, at the reference date of the 1st of December 2023. U INRIM - U BIPM = -0.04 µV; u c = 0.03 µV, at 1.018 V U INRIM - U BIPM = -0.18 µV; u c = 0.19 µV, at 10 Vwhere uc is the combined standard uncertainty associated with the measured difference, including the uncertainty of the realisation of the volt at the BIPM and at the INRIM, and the uncertainty related to the 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 CCEM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

Bilateral comparison of 1.018 V and 10 V standards between SASO-NMCC (Saudi Arabia) and the BIPM, September to November 2023 (part of the ongoing BIPM key comparison BIPM.EM-K11.a and b)

Main textAs part of the ongoing BIPM key comparison BIPM.EM-K11.a and b, a comparison of the 1.018 V and 10 V voltage reference standards of the BIPM and the SASO-NMCC (Saudi Arabia), from September to November 2023. Two BIPM Zener diode-based travelling standards (Fluke 732B), BIPM_E (ZE) and BIPM_F (ZF), were transported by freight to the SASO-NMCC and back to the BIPM. In order to keep the Zeners powered during their transportation phase, a voltage stabiliser developed by the BIPM was connected in parallel to the internal battery. At the SASO-NMCC and the BIPM, the reference standard for DC voltage is a Programmable Josephson Voltage Standard (PJVS). The output electromotive force (EMF) of each travelling standard was measured by direct comparison with the primary standard. The final result of the comparison is presented as the difference between the values assigned to DC voltage standards by the SASO-NMCC, at the level of 1.018 V and 10 V, at the SASO-NMCC, USASO-NMCC, and those assigned by the BIPM, at the BIPM, UBIPM, at the reference date of the 30th of September 2023. U SASO-NMCC - U BIPM = 0.06 µV; uc = 0.05 µV, at 1.018 V U SASO-NMCC - U BIPM = 0.22 µV; uc = 0.12 µV, at 10 Vwhere uc is the combined standard uncertainty associated with the measured difference, including the uncertainty of the realisation of the volt at the BIPM and at the SASO-NMCC, and the uncertainty related to the 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 CCEM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

Key comparison BIPM.RI(I)-K2 of the air-kerma standards of the PTB, Germany, and the BIPM in low-energy x-rays

Main textA key comparison has been made between the air-kerma standards of the PTB, Germany, and the BIPM in the low-energy x-ray range. The results show the standards to agree at the level of the expanded uncertainty of the comparison of 8.0 parts in 103. The results are analysed and presented in terms of degrees of equivalence, suitable for entry in the BIPM key comparison database.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 CCRI, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

Key comparison BIPM.RI(I)-K3 of the air-kerma standards of the PTB, Germany, and the BIPM in medium-energy x-rays

Main textA key comparison has been made between the air-kerma standards of the PTB, Germany, and the BIPM in the medium-energy x-ray range. The results show the standards to be in agreement at the limit of the expanded uncertainty of the comparison of 5.8 parts in 103. The results are analysed and presented in terms of degrees of equivalence, suitable for entry in the BIPM key comparison database.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 CCRI, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

Key comparison BIPM.RI(I)-K7 of the air-kerma standards of the BFKH, Hungary, and the BIPM in mammography x-rays

Main textA key comparison has been made between the air-kerma standards of the BFKH, Hungary, and the BIPM in mammography x-ray beams. The results show the standards to agree at the level of the expanded uncertainty of the comparison of 9.2 parts in 103. The results are analysed and presented in terms of degrees of equivalence, suitable for entry in the BIPM key comparison database.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 CCRI, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

Final report on EURAMET key comparison EURAMET.M.D-K2.2 (1523)

Main textThe key comparison EURAMET.M.D-K2.2 (1523)on the density of liquids determined by oscillation type density meters was organized and carried out within the framework of the EMPIR project 17RPT02 "rhoLiq". Density measurements of liquids are mainly performed by laboratories calibrating or checking liquid density measuring instruments such as oscillation-type density meters. Another aim of this comparison was to establish traceability for liquid density measurements at emerging National Metrology Institutes (NMIs) to enable them to provide high-level measurement and calibration services for national stakeholders, e.g. food, chemical, pharmaceutical and petroleum industries. The results of this comparison can be used to claim calibration and measurement capabilities (CMCs).Most European emerging NMIs in this project had not yet participated in comparisons or obtained unsatisfactory results, or the uncertainty had an unfit magnitude for purpose.BEV (Austria) piloted this comparison, supported by PTB (Germany).Samples of deuterated water, tetrachloroethylene and oil of high viscosity were measured in the temperature range from 5 °C to 20 °C at atmospheric pressure by hydrostatic weighing for this comparison.The coronavirus pandemic caused delays in the proposed initial schedule of this key comparison. Measurements were performed in 2021. The reference values of the key comparison were linked to CCM.D-K2 for PTB and EURAMET.M.D-K2 for BEV.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 CCM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

Supplementary comparison on a platinum resistance thermometer calibration from -70 °C to 250 °C

Main textThis supplementary comparison was about the calibration of platinum resistance thermometers in the range of -70 °C to 250 °C. Four laboratories participated in the comparison: Emirates Metrology Institute (EMI) from United Arab Emirates, SASO-NMCC from Saudi Arabia, QGOSM from Qatar and Tubitak UME from Türkiye. These Institutes are full or associated (Tubitak UME) members of the GULFMET Regional Metrology Organization.The pilot institute was Emirates Metrology Institute, who also provided the two transfer platinum resistance thermometers and monitor their stability during the comparison.The measurements of the comparison were performed between April 2019 and February 2021 and the circulation of the instruments was without problems, except for a delay of four months between the laboratories QGOSM and EMI due to the Coronavirus pandemic.The weighted mean of the measurements from all laboratories was used to produce the W ratios and R 0.01 reference values of the thermometers and no laboratory was excluded from this weighted mean. Note that this comparison is an RMO supplementary comparison, so the weighted mean values generated are used only as a baseline for reporting the results, and they have no particular meaning of reference values in the sense of the key comparisons.The results show a satisfactory agreement between the participating laboratories (|En| <1), except for two set-points: -35 °C and 100 °C, for one of the two transfer thermometers, for one of the laboratories. Combined expanded uncertainties for R 0.01 were equivalent to about 0.004 °C for the laboratories using water triple point cells as a reference, and 0.010 °C for QGOSM laboratory using ice point as reference. For the other measurement points, R values, were having equivalent combined expanded uncertainties ranging from 0.0060 °C to 0.010 °C for UME, 0.008 °C to 0.016 °C for EMI, 0.012 °C to 0.024 °C for SASO-NMCC and 0.014 °C to 0.054 °C for QGOSM. The mentioned uncertainties refer to the most stable of the transfer thermometers used in the 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 CCT, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

Final report for SIM.QM-S12: supplementary comparison for trace elements in natural water

Main textThe SIM Supplementary Comparison SIM.QM-S12 for Trace Elements in Natural Water was undertaken to assess and demonstrate the analytical capabilities of national metrology institutes (NMIs) and designated institutes (DIs) of SIM members (or other regions) for the accurate determination of trace elements in natural water at µg/kg levels.Evidence of successful participation in formal, relevant international comparisons is needed to document calibration and measurement capability claims (CMCs) made by NMIs and DIs.Seventeen NMIs and DIs participated. Participants were requested to evaluate the mass fractions, expressed in µg/kg, of arsenic, cadmium, lead and antimony in a natural mineral groundwater that was spiked with the respective elements. A variety of instrumental techniques including inductively coupled plasma mass spectrometry (ICP-MS), isotope dilution ICP-MS (ID-ICP-MS), inductively coupled plasma optical emission spectrometry (ICP-OES), electrothermal atomic absorption spectrometry (ETAAS) and hydride generation flame atomic absorption spectrometry (HG-FAAS) were used by the participants for the determination.The NIST decision tree was used to assign the SCRV estimate for the proposed measurands and to calculate the degrees of equivalence of each national measurement standard following the IAWG Guidance on Using NIST Decision Tree for Comparison Reporting from 30 June 2023.Successful participation in SIM.QM-S12 demonstrates measurement for determination of elements in water matrices. Considering the IAWG Core Capability Matrix, this material falls into the matrix challenge called "Water/aqueous", which corresponds to the CCQM amount-of-substance category fresh water, and so will support CMCs for the metalloids and semi-metals at mass fraction levels below 50 µg/kg (As and Sb measurements) and transition elements at mass fraction levels below 50 µg/kg (except Hg) (for Cd and Pb measurements).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 CCQM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

Report of subsequent key comparison CCQM - K73.2018.2 amount content of H+ in hydrochloric acid (0.1 mol/kg-1)

Main textThe subsequent key comparison K73.2018.2 was performed to demonstrate the capability of the participating institutes to measure the amount content of H+ in hydrochloric acid as a follow-up of the previous key comparison CCQM-K73.2018. A HCl solution of a slightly different composition to that in CCQM-K73.2018 was used.There were two institutes and SMU as the coordinating laboratory participating in this subsequent comparison. UkrCSM obtained results in good agreement with the reference value; INMETRO results exhibited a large bias due to a calculation error found only after disclosure of the results.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 CCQM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

Supplementary comparison of the measurement of current transformers (CTs)

Main textThe purpose of conducting comparison COOMET.EM-S22 of reference measuring systems of the AC current ratio of national metrological institutes (NMIs) is to determine the degree of consistency of national standards among themselves in the participating countries.Six NMIs participated in the supplementary comparison COOMET.EM-S22. Affiliated Branch of D I Mendeleev Institute for Metrology (VNIIM-UNIIM), Russian Federation, acted as the coordinating laboratory of the comparison.The comparisons were carried out by comparing the measurement results of the characteristics of measuring current transformers (CTs), namely, the units of the coefficient and the angle of the scale conversion of the sinusoidal current at a frequency of 50 Hz.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 CCEM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

The CCL-K11 ongoing key comparison. Final report for 2023

Main textSix lasers from six national metrological institutes (NMIs) were compared in the year 2023 as part of the CCL-K11 ongoing key comparison, initiated by the 13th meeting of the Comité Consultative des Longueurs (CCL) in 2007. The absolute frequency of theses lasers was measured in three different node laboratories following the technical protocol for CCL-K11. All are practical realisations of the definition of the metre according to the MeP for the definition of the metre.Five standards are He-Ne-lasers stabilized on the f component of the R(127) 11-5 transitions of molecular iodine 127I2 with a wavelength of approximately 633 nm.The sixth standard is a fibre laser stabilized to the P(16) (ν1+ν3) transition of molecular acetylene 13C2H2 with a wavelength of approximately 1542 nm. The technical protocol was deliberately designed to accommodate artefacts of different wavelengths in a common framework.The results of these measurements are compiled in the present report. The comparison reports, as communicated by each participant, are included in the main document.This document constitutes the thirteenth final report for the ongoing key comparison CCL-K11.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).

Comparison of liquid density measurements among SIM NMIs - SIM.M.D-S7

Main textThe aim of this comparison was to compare measurement results on liquid density at 20°C and at atmospheric pressure among National Metrology Institutes (NMIs) belonging to the Inter-American Metrology System (SIM, by its acronym in Spanish).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 CCM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

PAWG pilot study on quantification of total haemoglobin in blood

Main textUnder the auspices of the Protein Analysis Working Group (PAWG) of the Comité Consultatif pour la Quantité de Matière (CCQM) a pilot study, CCQM-P201, was organised. Five National Metrology Institutes (NMIs) participated in this pilot study and provided a total of eleven measurement results using six different methods based on three different measurement principles. The purpose of this pilot study was to develop measurement capabilities for the accurate quantification of intact haemoglobin (Hb) whereby measurement results could be made directly traceable to the SI. The choice of protein resulted from its ability to be quantified via different measurement principles providing different routes of traceability. Hb also provided a model of an intact protein with a complex tetrameric structure which is often measured via quantification of a specific subunit or the incorporated haem group. To achieve appropriate results for the chosen measurand, it was necessary to distinguish between the whole protein and fragments of the tetrameric structure, such as dimers or monomers. The participants were encouraged to investigate several of the measurement methods available. This was considered particularly advantageous in this instance as various methods applied to the same analyte may assist in identifying possible previously unknown biases or interferences of the various methods. Hb is being used as a model system to build capacity in methods for the quantification of proteins with a molar mass ≤ 100 kDa in biological fluids in a concentration range > 1∙106 pmol/g.This was the first pilot study for the quantification of an inherent protein in blood with all the natural variations that protein shows in a clinical sample. The different methods applied by the participants included isotopic dilution (ID) organic mass spectrometry (MS) of specific peptides after tryptic digestion, species-specific ID inductively coupled plasma mass spectrometry (ICP-MS), post-column ID ICP-MS, quantification via total iron after chromatographic isolation of Hb and acid digestion as well as two optical methods. One of the latter was the reference method proposed by the International Committee for Standardisation in Haematology (ICSH) based on the conversion of Hb to hemiglobincyanide (HiCN), the other used the conversion of Hb with alkaline haematin detergent both followed by the measurement of spectroscopic absorbance.Considering the use of very different measurement techniques for the quantification of total Hb, the results are in good agreement with a reference value with corresponding expanded uncertainty of (120.6 ± 1.2) mg/g calculated as DerSimonian-Laird mean. However, the observed differences between the results are not completely reflected in the reported measurement uncertainties. The calculated interlaboratory standard deviation or Tau value (dark uncertainty) was approximately 3 % whilst the average reported measurement uncertainty was approximately half this (1.4 %). A possible reason for this large difference may lie in the underestimation of any necessary conversion factors and their uncertainty contributions, between the target analyte measured and the requested measurand.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 CCQM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).