Accuracy of SKiNN emulation of υ_rms maps in a typical case (top) and in a particularly poor case (bottom). The first two columns give the truth and predicted υ_rms maps. Residual differences (third column, km s⁻¹) and relative residuals, evaluated as (prediction–truth)/truth (fourth column) are also plotted. Where pixels have zero values, relative residuals are shown in orange. The black circle corresponds to a 2″ radius, inside which real data are most constraining.