FWHM visibility fitting for two single exposures. The coloured dots with error bars show the visibilities measured at different baselines. The best-fitting results from Eq. (1) are shown as black solid lines; the grey shaded regions show the 1σ fitting uncertainties. The dates and the UTC time are shown in the bottom left corners of each panel. The left panel illustrates a typical exposure, while the right panel shows an example of poor-quality data.