Effect of single-dish telescope beam size on the spectral lines of three models is shown. The telescope beam size is simulated by a normalised Gaussian filter. The total flux of the spectral lines is therefore scaled by the normalisation factor , with . In effect, this means that the peak flux of the line (in the plot) scales with beam resolution. This is done to emphasise the evolution of the line shape. Left panel: effect of a decreasing beam size on the face-on reference model, which creates a trident shaped profile. Middle panel: effect on the edge-on reference model, which forms a very explicit double-peaked profile. Right panel: beam-size effect on a low mass-loss, Σ = 1, face-on shell spiral. Here the double-peaked character of the spectral line is preserved.