The residual velocity offsets with respect to z_sys before, three leftmost panels, and after, three rightmost panels, correction are presented against our regression parameters. The corrected method displayed refers to Correction 4 without outliers reported in Table 7. Squares (circles) represent data from M17 (UKIRT; this work). The outliers discussed in Section 3.1 do not appear in this plot given their abnormally large velocity offsets.