Position of CPD −57° 3509 in the N/O-N/C diagram (by mass): present work (black dot) and the result from Hunter et al. (2009, open circle), compared to 29 early B-type stars from Nieva & Simón-Díaz (2011) and NP12 (grey dots). An error bar typical for the latter is indicated in the upper left corner. The dashed line indicates the analytical approximation to the nuclear path for CN-cycled material using CAS values (Przybilla et al. 2010).