(u, v) coverage of M87* during the 2017 (left), 2018 (middle), and 2021 (right) campaigns for the band 3 (227.1 GHz) observations. The ticks show each year’s interferometric EVPA and the colour of the observed interferometric fractional linear polarization, after de-biasing for thermal noise and applying leakage corrections. The leakage terms used are the fiducial values from EHTC (2021a) in 2017 and the THEMIS leakage solutions in 2018 and 2021. The clusters of high polarization fractions in 2018 come from the GLT, which was underperforming in 2018 due to an incomplete commissioning at that time, as described in Koay et al. (2023a).