Average carbon isotope ratios in clump stars of open clusters as a function of stellar turn-off mass. The results of this work are marked by filled squares; from Mikolaitis et al. (2010, 2011a,b) and Tautvaišiene et al. (2000); Tautvaišienė et al. (2005) – open squares; from Smiljanic et al. (2009) – open triangles; from Luck (1994) – reversed open triangle; from Gilroy (1989) – open circles. The models of the first dredge-up, thermohaline mixing (TH) and rotation-induced mixing (V) are taken from Charbonnel & Lagarde (2010). The CBP model of extra-mixing is taken from Boothroyd & Sackmann (1999). A typical error bar is indicated (Charbonnel & Lagarde 2010; Smiljanic et al. 2009; Gilroy 1989).