Average of the computed dipole (ℓ = 1) period spacings () assessed in the range of the periods observed in J1518, corresponding to each WD model sequence considered in this work, in terms of the logarithm of the effective temperature. Numbers along each curve denote the stellar mass (in solar units). The observed period spacing derived for J1518 is depicted with a horizontal solid line. We also indicate the T_eff (vertical solid line) in the 3D model, together with its uncertainties (vertical dashed lines).