Decrease in the dispersion (in percent) of the original or residual global gas metallicity once the subsequent relation with different galaxy properties (x-axis) was modelled (with a spline function on binned values) and removed. This exercise is accumulative, so the modelled relation was subtracted to the residuals from the previous one. The secondary x-axis (top) shows the case when we forced the stellar mass to be the first parameter to model (orange line).