Set of 1000 MCMC HARPS instrumental profiles, trained on the data and shown on a fine grid. For each profile, we calculated the median, the mean, the mode, and the location satisfying ψ(−0.5) = ψ(0.5), producing distributions for each of the four quantities. The means of the four distributions is shown as a vertical line of different colour and stroke. The x-axis zero point is set to the mean of the distribution for ψ(−0.5) = ψ(0.5) centres. The inset on the top right shows a zoom-in of the region around the profile peak. Units in the inset are the same as in the main panel.