Comparison of the observational HR diagram in the MG vs. (B−V) plane for the Hipparcos stars in Gaia DR1, using their Hipparcos (van Leeuwen 2007) parallaxes (a) and their parallaxes as listed in Gaia DR1 (b), c)). The relative standard uncertainties on the parallax are less than 20% for both the Hipparcos and Gaia DR1 parallaxes in panels a) and b), while in panel c) all stars with relative parallax uncertainties better than 20% in Gaia DR1 are shown. The stars were otherwise selected as described in the text. All panels show the stars as individual symbols where possible and where the symbols overlap the relative source density is shown, with colours varying from purple (dark) to yellow (light) indicating increasing density on a logarithmic scale. The contours enclose 10, 30, and 50 per cent of the data.