M 87 amplitudes on the left and phases on the right as a function of baseline length (u-v distance), color-coded by baselines. Top panels: visibilities after the model-agnostic rPICARD calibration (before self-calibration). Middle panel: model data from the final image of the imaging plus self-calibration cycles, shown in Fig. 6. Bottom panel: data after the last round of self-calibration. In the model-agnostic calibration, anomalously high amplitudes are due to station gain errors; the system temperature measurements of the Fort Davis and Owens Valley stations were doubtful. Large residual phase trends are related to low S/N measurements, where long fringe fit solution intervals are chosen by rPICARD. These amplitude and phase trends are both corrected for with the iterative self-calibration.