Comparison of cooling tracks of 0.2  M_⊙ (dashed lines), 0.5  M_⊙ (solid lines) and 1.2  M_⊙ (dotted lines) WDs, between the models from the Althaus group (dark blue lines) and the Bergeron group (light blue lines). The 3 lines that represent cooling tracks from the Althaus models correspond to 3 WDs with different core compositions: He for the 0.2  M_⊙ WD, CO for the 0.5  M_⊙ WD and ONe for the 1.2  M_⊙ WD, whereas the 3 lines from the Bergeron models all correspond to WDs with a CO core. The age of the universe is indicated with a vertical thin black line.