Abundance of carbon A(C) vs. [Fe/H] in dwarfs and turnoff CEMP stars, following Sivarani et al. (2006, their Table 4), [orange open squares]), Frebel et al. (2005, 2007) [blue open squares], Thompson et al. (2008) [green open circle], Aoki et al. (2009) [blue open diamonds], Behara et al. (2010) [full orange circles], Placco et al. (2011) [blue ×), Carollo et al. (2011) [blue +], Masseron et al. (2010, 2012) [full green squares], Yong et al. (2013b) [blue open triangles]. Our measurements are represented with full red circles. The dashed blue line (representing [C/Fe] = +1) separates the region of the carbon-rich metal-poor stars from the region of the normal metal-poor stars (hatched). When [Fe/H] is higher than –3 the carbon abundance is almost constant and close to 8.25 (see also Masseron et al. 2010). For [Fe/H] < −3.4 the carbon abundance drops suddenly to about 6.5. However, it is difficult to decide whether at very low metallicity A(C) is also constant, or whether the line A(C)= 6.5 represents an upper limit of the carbon abundance in these extremely metal-poor star (Masseron et al. 2010).