Evolution of surface abundances of boron and nitrogen and rotational velocity in a 12 M_⊙ stellar model with v_{rot, i} = 200 km s⁻¹ during the main sequence evolution. Three panels show the effects of varying rotational mixing efficiency f_c (left), degrees of inhibition by chemical gradient f_μ (middle), and degrees of angular momentum transport f_ν (right). The reference values are f_c = 0.033, f_μ = 0.1, and f_ν = 1.0, and one of the three is changed in the presented models.