Squared visibilities obtained for HD 142527. Left: squared visibilities obtained with PIONIER on two nights using equal baselines. Right: squared visibilities obtained with AMBER on two other nights using equal baselines. The error bars in vertical direction give the uncertainties of the squared visibilities. In a horizontal direction, the bars indicate the spectral bins. Spectrally resolved measurements are averaged according to Eq. (4), where the mean values are plotted as solid lines and the corresponding uncertainties (Eq. (5)) as shaded rectangles.