Same definitions as for the symbols in Fig. 1 for the correlation diagram of candidate C₂ DIBs and possible C₂-related DIBs. The horizontal axis displays the average Pearson correlation factor, knq_C2 (Eq. (3) and Fig. 1). The vertical axis displays the ratio of the DIB equivalent widths in the sight line of HD 204827 to HD 183143 (Eq. (1); actual values or equivalent values, see Appendix B.3). The selection criteria (Eqs. (4,6); dotted blue lines) distinguish C₂ DIBs well from ζ DIBs. Most C₂ DIBs and related DIBs have R₂₁ ≥ 1.5. See Fig. B.2 for an extended version of this figure, including DIB labels.