Mass–temperature diagrams of the GSPC cool white dwarfs within 100 pc of the Sun. The top panel shows the diagram for DA stars, and the bottom panel shows the non-DA stars. Also shown as solid black curves are theoretical isochrones, labeled in units of Gyr, obtained from cooling sequences with C/O-core compositions, q(He) = 10⁻², and q(H) = 10⁻⁴. The lower blue solid curve indicates the onset of crystallization at the centre of evolving models, and the upper one indicates the locations where 80% of the total mass has solidified. The dashed line indicates the fiducial mean mass of 0.6 M_⊙.