Scheme of the process. In step 1, three averaged profiles coming from three different data sets, together with the FalC model,are used to calculate the oscillator strengths of three spectral lines. In step 2, pixel-by-pixel inversions are done using the oscillator strengths of the three spectral lines calculated previously and the data set with the highest quality to determine the oscillator strengths of 15 spectral lines. In step 3, step 2 is repeated but taking into account 15 spectral lines in the inversions to redetermine the oscillator strengths of all the spectral lines.