Expansion distances, D_exp, of PNe versus the trigonometric Gaia D_DR2 distances (Cols. 3 and 4 of Table 1). The dashed line is the error weighted linear regression forced to go through the origin (Eq. (6)). The dotted line represents the corresponding linear regression for the eight objects with D_DR2 < 2 kpc only (Eq. (7)). The 1:1 relation is given for comparison as well (solid). For the red objects (IC 2448, NGC 5882, NGC 7662), discrepancies between the terrestrial and Gaia photometry of the central star exist (see text for details).