Bottom diagram: comparison between the EWs measured using the Gaussian processes (GP) and EWs coming from a simple χ² analysis. EW measurements for the line at 8498 Å are not shown. The inset shows the histogram of the uncertainty ratios. Brighter colors of the dots correspond to higher ratio values. Top diagrams: histograms of the differences between the ith and the jth repeated observation for the lines at 8542 Å and 8662 Å. The black histogram includes the measurements generated by Gaussian processes, the gray histogram shows the χ² derived values. Gaussian distributions with equivalent standard deviations Σ are overplotted, which should ideally be equal to 1.