estimates which were, on the whole, somewhat lower than has proven to be justified on the basis of recent high-resolution spectroscopy, in particular for the hotter stars near the main-sequence turnoff of an old halo population.

The re-calibration of metallicity estimates based on medium resolution spectroscopy described by Beers et al. (1999) avoids, to a great extent, the above difficulties. This re-calibration makes use of an additional metallicity estimator based on the Auto-Correlation Function of metallic lines in a stellar spectrum (originally described by Ratnatunga & Freeman 1989), which provides a superior estimate of abundance to CaII K in the regime $\feh >
-1.0$. The combination of the CaII K and ACF approaches implemented in Beers et al. (1999) results in metallicity estimates over the interval $-4.0 \le \feh
\le 0.0$ with typical errors on the order of 0.1-0.2 dex, and no significant systematic offsets.

Figure 1 is a comparison of the abundance determinations of the HK survey stars in the revised catalog based on the new and old calibration. Note that the broad sloping region about the one-to-one line, which is dominated by stars with $0.3 \le (B-V)_o \le 0.5$, indicates that the revised abundances for the hotter HK 