Correlation diagram for 79 χ_a DIBs (Table C.1) and 43 χ_b DIBs (Table C.2), compared with C₂ reference and candidate DIBs and C₂-related DIBs (Tables B.3–B.4), and reference main ζ, ζσ and σ DIBs from Fan et al. (2022). The vertical axis displays the ratio R21 of the DIB equivalent widths in the sight line of HD 204827 to HD 183143 (actual values or equivalent values, see Appendix B.3). In the top (resp. bottom) panel, the horizontal axis displays the anticorrelation factor, kn₆₀₁₀, equivalent to kn₆₀₀₉ (resp. q₆₀₁₀, equivalent to q₆₀₀₉) (excluding the sight lines of HD 175156 and HD 148579). The comparison of the top and bottom panels visualises the difference between kn₆₀₁₀ and q₆₀₁₀.