We have used main-sequence fitting to calibrate the distances to the globular clusters NGC 6397 , M5 , NGC 288 , M71 and 47 Tucanae , matching the cluster photometry against data for subdwarfs with precise Hipparcos parallax measurements and accurate abundance determinations .
Both the cluster and subdwarf abundance scales are tied to high-resolution spectroscopic analyses .
The distance moduli that we derive for the five clusters are 12.24 , 14.52 , 15.00 , 13.19 and 13.59 magnitudes , with uncertainties of \pm 0.15 magnitudes .
As in previous analyses by Reid ( 1997 ) and Gratton et al ( 1997 ) , these distances are higher than those derived in pre-Hipparcos investigations .

The calibrated cluster colour-magnitude diagrams provide fiducial sequences in the ( M _ { V } , ( B - V ) ) plane , outlining the distribution expected for stars of a particular abundance .
We have combined the photometric data for NGC 6397 ( [ Fe/H ] =-1.82 dex ) , M5 ( -1.10 dex ) and 47 Tucanae ( -0.70 dex ) with the mean colour-magnitude relation delineated by nearby FGK dwarfs to define a reference grid in the ( M _ { V } , ( B - V ) ) plane , and we have matched this grid against data for stars drawn from the Lowell proper motion survey , with both Hipparcos astrometry and abundance determinations by Carney et al ( 1994 ) .
Limiting the comparison to non-binaries , there are significantly fewer subluminous stars than expected given the spectroscopic metallicity distribution .
Inverting the analysis , this implies a reduction by a factor of three in the proportion of stars contributing to the metal-poor ( [ Fe/H ] < -0.4 ) tail of the Galactic disk .
We discuss the implications of these results .