Velocity corrections for uneven slit illumination in PV diagrams along the jet averaged across the jet axis for exposure 1 (top) and exposure 2 (bottom). Black histograms plot the theoretical correction computed for a 2D brightness distribution fitted by a Moffat function. Symbols with error bars show empirical shifts obtained from cross-correlation of telluric absorption features against the reference spectrum (at Y = 0″ in exposure 1 and in exposure 2). To ease comparison with the theoretical model, they are shifted vertically to match the model at the reference spectrum position.