For the same range of S/N values as in Figs. 10 to 12, line width at the 50% height for the raw spectrum versus the same for the fitted profile is compared. DDO 53 is shown here. The square symbol indicates the mean value for the raw spectra, the triangle the mean for the fitted profiles. These respective points have been slightly offset horizontally for clarity. The halftone line indicates the value for the profile fitted to the original THINGS data.