Correlation between the [Si/Ti] and [Zn/Fe], using the measurements of Berg et al. (2015), illustrate the effect of dust depletion. Si and Ti are both α elements, but Ti is more refractory than Si. The measurements are not expected to lie on the one-to-one (dotted) line. The slope depends on the relative depletion of Si with respect to Ti, and, on the other hand, on the relative depletion of Zn with respect to Fe, which are independent from each other. The outlying data point is Q 0013-004 (SDSS 0016-0012), for which Herbert-Fort et al. (2006) remarked that the Ti measurement is not reliable and likely a misunderstanding (velocity profile spanning ~1000 km s^-1).