Surface nitrogen abundance for the sample stars divided into two mass bins (lower masses, left; higher masses, right) to enable better visibility, as a function of projected rotational rate and plotted against the current Geneva and Bonn tracks with rotation (upper and lower panels, respectively). Symbol coding distinguishes between objects of different LC; magnetic stars are additionally highlighted by large squares. Colour coding is used to denote the morphologically peculiarly objects with very weak nitrogen lines (grey), and the stars whose predicted and observed [N] values differ by less (yellow) or more (green, orange) than 1σ. The observed v sin i accounts for the effects of macroturbulence; the model V_rot has been multiplied by π/4 to take the average projection effect into account (e.g. v_init ≈ 300 km s⁻¹ corresponds to v sin i ≈ 240 km s⁻¹). Upper panels: coloured parts of some tracks represent the dwarf (log g > 3.75, red) and the giant (3.75 < log g < 3.6, blue) phases, respectively.