  Abundances of the volatile elements S and Zn have now been measured in around
80 individual stars in the Sculptor dwarf spheroidal galaxy, covering the
metallicity range $-2.4\leq\text{[Fe/H]}\leq-0.9$. These two elements are of
particular interest as they are not depleted onto dust in gas, and their ratio,
[S/Zn], has thus commonly been used as a proxy for [$\alpha$/Fe] in Damped
Lyman-$\alpha$ systems. The S abundances in Sculptor are similar to other
$\alpha$-elements in this galaxy, consistent with S being mainly created in
core-collapse supernovae, but also having some contribution from supernovae
Type Ia. However, our results show that Zn and Fe do not trace all the same
nucleosynthetic production channels. In particular, (contrary to Fe) Zn is not
significantly produced by supernovae Type Ia. Thus, [S/Zn] cannot be reliably
used as a proxy for [$\alpha$/Fe]. We propose [O/S] as a function of [S/H] as a
possible alternative. At higher metallicities, the values of [S/Zn] measured in
Damped Lyman-$\alpha$ systems are inconsistent with those in local dwarf
galaxies, and are more compatible with the Milky Way disk. Low-metallicity
Damped Lyman-$\alpha$ systems are, however, consistent with the most metal-poor
stars in Local Group dwarf spheroidal galaxies. Assuming that the dust
depletions of S and Zn are negligible, our comparison indicates that the star
formation histories of Damped Lyman-$\alpha$ systems are on average different
from both the Milky Way and the Sculptor dwarf spheroidal galaxy.
