Evolution of the spin period of a spinning-down NS with constant baryon mass M_b = 2.325 M_⊙ (black lines) and M_b = 2.3 M_⊙ (blue lines), in relation to Fig. 4. The time unit is normalized by the value of the magnetic dipole moment μ_B = BR³ = 10³⁰ [cgs], which corresponds to a magnetic field of B = 10¹² G and a stellar radius of R = 10 km. The lines after the mini-collapse related to a sudden spin-up and marked with red arrows are denoted according to the assumption that the B field stayed unchanged (solid lines), decreased twice (to B = 5 × 10¹¹ G, dashed lines), or decreased by one order of magnitude (to B = 10¹¹ G, dash-dotted lines). Dotted lines mark the evolution of a system with a purely quadrupolar magnetic field of B = 10¹² G, emulating a drastic change of the field structure after the mini-collapse.