Illustration of the iteration process in a given Chebyshev polynomial order for an early-type star (top) and a late-type star (bottom), focussing on the wavelength range [3750, 5000] Å. Top: order 26 for HD 3901 with spectral type B2V. Bottom: order 16 for HD 41116 with spectral type G5III. The successive polynomial fits start with the thick black line, representing the first iteration, and progress towards the green line, representing the iteration with the best d score. For the sake of completeness, the iterations corresponding to the best p and n scores are represented as well, in red and blue respectively. The final selection is based on d, combining p and n.