Surface boron abundances of the sample of stars studied by Jin et al. (2024) as a function of the surface gravity, colour-coded according to their v sin i. Left: Predictions of models without magnetic fields at v_ini/v_crit = 0.1, 0.2, 0.3 and 0.4. Right: Models with magnetic fields at the same velocities. Tracks with green, blue and black outlines, correspond, respectively, to models of 9, 12 and 15 M_⊙. The majority of the tracks were computed until the end of core hydrogen burning. The 15 M_⊙ magnetic models with v_ini/v_crit = 0.3, 0.4 were further evolved until central helium fractions of 0.87 and 0.78, respectively (see also Fig. C.1). Stars without an upper errorbar only have an upper limit on the boron abundance.