Observed CH⁺(835 GHz) line characteristics (Table B.1) vs. object parameters given in Table 1. Only the line component in absorption is shown. L 1489 is not included in the correlation coefficient ρ, given where statistically significant. The symbols indicate different types of objects: Red diamonds for Class 0, yellow triangle up for Class I (L 1489), brown circle for intermediate mass, light blue triangle down for high-mass mid-IR quiet (NGC 6334 I(N)), green square for high-mass mid-IR bright and hot molecular core, and dark blue triangle left for high-mass ultra-compact HII (NGC 7538 IRS1).