Top: position-velocity plots for the approaching lobe of the Class 0 bipolar jet HH 212, NK1 knot, in [Fe ii] and H₂ emission, where positive distances correspond to south-east; bottom: radial velocity profile across the jet in the spatially resolved H₂ emission, and a plot of the differences in the Doppler shift, Δv_rad, between one side of the jet knot and the other. However, caution must be taken in its interpretation given that the emission intensity is asymmetric in the position direction.