Temperature residuals versus number of nodes for different inversion schemes. Top row: empirical cumulative distribution functions of the absolute residuals Eq. (3) of the schemes i1 (solid green), i2 (dashed blue) and i7 (dashed-dot red) for different number of temperature nodes at three selected optical depths in the chromosphere; bottom row: corresponding median (circle markers) and the interval (vertical lines) containing 90% of the distribution of absolute residuals.