Upper left: average observed and synthetic profiles in the region. Upper right: sample profiles where the χ² is equal to the median in the region. Lower left: profiles representative of a good reconstructed fit, where the χ² is equal to the median minus one standard deviation. Lower right: profiles representative of a poor reconstructed fit, where the χ² is equal to the median plus one standard deviation. In all cases, the profile in blue is the observation and orange is the synthesis from the reconstructed model atmosphere (reconstructed fit).