CCL-K3.n01: Angle standards : optical polygon

At its meeting in 2014, the Consultative Committee for Length (CCL) WG-MRA decided upon a key comparison on the measurement of angle standards. Initially the comparison was to include both optical polygons and angle encoders, however, the comparison was eventually scaled back to only include optical polygons. The comparison was also delayed due to a change in pilot laboratory, and artifact circulation was started in April 2023 and completed in September 2025. Two optical polygons by different manufacturers were circulated: a 12-sided polygon similar to one used in the EURAMET.L-K3.n01 comparison, and a 10-sided polygon similar to the polygon used in the SIM.L-K3-2019 comparison. Unfortunately, the 12-sided polygon was not stable for the duration of the comparison and an additional artifact stability term was added in quadrature to the participants 12-sided polygon reported uncertainties. The vast majority of participants successfully supported their uncertainty claims.