Carbon isotopic ratios in model yields (large circles and colour bar) and observations (small grey points) versus metallicity. The [Fe/H] ≃ −1 models are from Fishlock et al. (2014) for initial masses ≤6 M_⊙, and from Doherty et al. (2014b) for initial masses ≥7 M_⊙. [Fe/H] ≃ −2 models are from Karakas (2010) for initial ≤6 M_⊙, and from Doherty et al. (2014b) for initial masses ≥7 M_⊙. [Fe/H] ≃ −3, −4, −5, −6 and −8 models are from Campbell & Lattanzio (2008) for initial masses ≤3 M_⊙, and from GP21 for initial masses ≥3 M_⊙. The observed ratios are from the SAGA database (Suda et al. 2008).