UVES spectrum of Galactic main sequence star HD 41297. Panel a shows the order-merged non-normalised spectrum extracted with the ESO data reduction pipeline. Panels b, c, and d demonstrate the spectra normalised by fitting a low-degree polynomial to the individual échelle orders, fitting a 2D smoothing spline to all 30 échelle orders in the UVES blue arm, and iterative fitting of synthetic spectra, respectively. The best-fit synthetic spectrum obtained for this star is shown in panel e for comparison. See text for details.