Mass of accreted matter as a function of the time needed to spin-up the progenitor NS to the observed properties of PSR J1614−2230 (i.e., M, B, and f) for the five models indicated in Table 3. The dot corresponds to a spin-up track proceeding at a rate equal to the Eddington accretion rate Ṁ_Edd ~ 3 × 10^-8M_⊙/ yr; the accretion timescale is then ~2 Myr. For tracks with τ_acc ≲ 2 Myr, Ṁ is greater than Ṁ_Edd.