ESPRESSO transmission spectrum of WASP-178 b on the planetary rest frame around the Na I doublet. Top panel: the grey points represent the unbinned data, the blue points represent the data binned by x20 and the Gaussian fit to the sodium doublet lines is shown by the solid red line. The expected line centres are marked by the dashed black lines. Bottom panel: the residuals of the fit are shown, with the black dots corresponding to the binned data.