Surface elemental abundances of main sequence stars as a function of luminosity for nitrogen (left) and boron (right). The upper panels show single stars, while the lower panels show mass gainers. The x-axis represents log(N/N_i), where N is the elemental number fraction and N_i is the initial value. Abundances are sampled at 0.1 Myr intervals for all models within the main sequence band during the core hydrogen burning phase. Data points are stacked such that those with higher Y_s appear above those with lower Y_s. For single stars, lines indicate the limits for different initial rotational velocities. For mass gainers, the line for 400 km s⁻¹ is shown.