Histogram (N = 406) and box-and-whisker plots for the deviation between MR-MP valence level energies and the recommended values in the NIST online database (Kramida et al. 2018) for L-shell ions of Fe. The annotations show the statistical parameters determined using the method of Tukey (1977): first (Q1), second (Q2), and third (Q3) quartile; lower (LIF) and upper (UIF) inner fences; and lower (LOF) and upper (UOF) outer fences.