SIMBAD references

We have used the observed radial velocities of planetary nebulae, and the galactic rotation curve to define a new distance scale for planetary nebulae. Care has been taken to restrict the analysis to sources in which distance non-linearities are minimised, and for which distortion of the distance scale is likely to be small. We conclude, as a result, that the so-called ``long'' distance scales are the most valid, and that various ``shorter'' scales are unlikely to be correct. The primary systematic errors in this procedure derive from uncertainties in the galactic rotation profile, and in Θ₀ and R₀. Such errors are less than those normally associated with PN distance determinations.