Comparison between the metallicity derived with the code HCm and the direct method, showing the consistency of our approach. The red dashed line is the 1:1 relation. At the bottom of the figure, the differences between the two methods are plotted as a function of the metallicity. The blue dashed line corresponds to the 0 level, while the blue continuous line is the median value. In the lower-right box, we have added the histogram with the distribution of the differences, with the median value line in green.