OPD residuals. Top panel: OPD residuals plotted against the S/N per baseline for all data collected from June to August 2023. The orange dots represent AT observations, and the blue dots denote UT observations. The dotted curve represents the theoretical limitation imposed by the measurement noise (λ/2πσ_j,k). The vertical dashed lines indicate the S/N observed with the UTs of a star at a given star magnitude. It should be shifted by about 2.5 magnitude for the ATs. Bottom panels: histogram of the same OPD residuals as in the upper panel for the ATs (left) and UTs (right).