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Report on the SIM Photometry and Radiometry Key Comparison of Spectral Regular Transmittance (SIM.PR-K6.2010)



Catherine Cooksey, Blaza Toman


This report details the results of the Inter-American Metrology System (SIM) key comparison on regular spectral transmittance (SIM.PR-K6.2010). Eight national metrology institutes participated in the comparison, which covered the spectral range from 380 nm to 1000 nm and the nominal transmittance range from 0.1 % to 90 % transmittance. The protocol mirrored that of the key comparison conducted by the Consultative Committee on Photometry and Radiometry (CCPR-K6.2010). The National Institute of Standards and Technology (NIST) served as the pilot. Each participant received a single set of 5 comparison (neutral density) filters to measure. The pilot measured all sets before and after the participant measurements. All measurements were completed between December 2016 and February 2018. The results of this comparison were linked to the key comparison reference value (KCRV) of the CCPR comparison and are expressed in terms of degrees of equivalence. While most of the participants can adequately measure spectral regular transmittance and evaluate its uncertainty, there are some cases of non-equivalence that will require further investigation on the part of the participants.


regular transmittance, key comparison


Cooksey, C. and Toman, B. (2021), Report on the SIM Photometry and Radiometry Key Comparison of Spectral Regular Transmittance (SIM.PR-K6.2010), Metrologia, [online],, (Accessed February 22, 2024)
Created September 10, 2021, Updated November 29, 2022