Toy model of line profiles originating in an expanding half annulus as a function of inclination to the observer. An inclination of 0° corresponds to the annulus expanding into the plane of the sky (IRAS 4B) and 90° corresponds to expansion along the line of sight (IRAS 2A). The incremental inclination is 10°. The inset shows the measured FWHM of the different profiles as a function of inclination, i.e., not obtained from a Gauss fit. The annulus expands at 15 km s^-1 and the internal velocity dispersion (FWHM) is 9 km s^-1.