1D profile of the [S ii]31/16 ratio along the flow, derived from integration of the line surface brightness across the jet and over each velocity interval. Horizontal dashed lines indicate upper and lower density limits on validity of the ratio as a n_e diagnostic. Empty symbols mark positions and velocities for which the modified BE-technique has been applied. Upper and lower limits arise when one of the lines is undetected, and so its flux has been set to 3σ.