Closure phase departures from zero or ±180° for all the observed stars and for all the wavelengths. For every data point, the lowest value between |data-0°|, |data-180°| , and | data+180°| is computed and normalised by the corresponding observed error, σ. β Oph is shown in the left panel, ϵ Cyg in the central, and HR 7633 in the right panel. The horizontal black line corresponds to the value of 1σ and the red line to 3σ.