Top: absolute value of the measured differential delay | AX_obs − c | for the demonstration run as a function of hour angle. Normal mode data are shown in red and swapped mode data in blue. Middle: rectified residuals of the astrometric fit. Open and filled symbols indicate scanning and tracking data, respectively. File-average bins are shown in black. Bottom: rectified and binned residuals with error bars that rely on Gaussian statistics (error of the mean).