Ratio of α elements to iron for the programme stars (red stars) compared to those measured by our group in other EMP dwarf stars (Bonifacio et al. 2009, 2012; Caffau et al. 2011c, 2013a,b). Black squares are measurements from X-shooter spectra, while black hexagons are measurements from UVES spectra. In the panel giving the [Ca/Fe] ratio, the blue star symbols are Ca II measures. We restricted the x-axis so as to exclude SDSS J1035+0641; which only has an upper limit on iron and thus a lower limit on [Ca/Fe] and is not informative.