Standard deviation over time of squared visibilities (20% frames selection, solid line) and of rescaled differential squared visibilities (dashed line) for each wavelength per exposure file and for dataset AT-LR-FT. The parameter is averaged over the three baselines and over the different exposure files of the dataset. The lower statistical dispersion of the differential squared visibility compared to the absolute one appears clearly in this figure. The mean values of over wavelengths are presented in Table 2 for all the datasets.