Difference between present and initial surface abundance as a function of surface gravity. Top, middle, and bottom rows show differences in nitrogen, carbon, and oxygen abundances respectively. The Geneva, Bonn, and Stromlo models are shown in the left, middle, and right column respectively. For each set of models the 25 and 40 M_⊙ tracks are shown by the dashed and dotted lines respectively. Green, magenta, and blue lines correspond to Galactic, LMC, and SMC chemical composition.