Abundance ratios [S_NLTE/Mg] with [Mg/H]. Grey squares show Galactic halo stars with S measurements from Spite et al. (2011), and Mg from Andrievsky et al. (2010). Circles, pentagons, and hexagons show the target stars in Sculptor; the most iron-poor stars ([ Fe / H ] ≤ −1.7) as dark blue circles, the most iron-rich (−1.3 ≤ [ Fe / H ]) are shown as cyan hexagons, and other stars as blue pentagons. Note that in Sculptor, the Mg abundances have not been corrected for NLTE effects. However, these are expected to be small (and positive) for the target stars (≲0.1 dex).