Example of the functional forms fitted to the rotational velocities and molecular gas surface density profiles (in this case for the galaxy IC 5273). Left: Observed rotation curve (grey markers with error bars) and the best-fit model (solid blue curve) with its 1σ and 2σ uncertainties represented by the shaded region. Right: Molecular gas surface density profile assuming our master α_CO conversion factor (grey markers with error bars). The best-fit model is shown as a solid red curve, with its 1σ and 2σ uncertainties indicated by the shaded region. Profiles derived using alternative CO-to-H₂ conversion factors (S20, MW, N12) are overplotted for comparison (B13 was not available for IC 5273). As can be seen, our profile represents a good compromise between the different calibrations and incorporates realistic uncertainties.