Final report on supplementary comparison EURAMET.L-S20: Comparison of laser distance measuring instruments

The results of the supplementary comparison EURAMET.L-S20 of laser distance measuring instruments (EDMs) are reported. It was the first comparison of EDMs. Four EDMs were circulated among 13 European NMIs. Each EDM was calibrated at a distance of 0.3 m and at regularly spaced intervals every 5 m for a range up to 50 m. The measurements were conducted between 2011 and 2012. The test of the stability of the EDMs showed significant changes in the mean results over timescales of months or even days. The uncertainty of the results mainly comes from the uncertainty due to the reproducibility, and it is difficult to distinguish the part relevant to the laboratories' calibration and measurement capabilities. For the analysis both the deviations from the reference value and the En numbers were calculated. For the evaluation of the reference value, the weighted mean approach has been chosen, although the consistency check failed in many cases. A more complicated procedure for the evaluation of the reference value was proposed, which slightly changes the uncertainty of the reference value. Most results agreed within the claimed uncertainties. Some 4.7% of the results showed some larger deviations. Some participants may have a high percentage of values that are not compliant with their CMC claims due to the influence of the artifact and the estimation of its uncertainty.