Percentage deviations for BONNFIRES model sequences with fixed shell masses δm. The deviations are taken for nitrogen abundances at the time of the evolution when the difference between that evolutionary sequence against sequence with fixed δm = 0.02 M_⊙ is the largest. The model sequences are for a 20 M_⊙ star with initial equatorial rotational velocity of 300 km s^-1 with fixed timestep δt = 0.1 Myr.