We demonstrate that low resolution Ca II triplet ( CaT ) spectroscopic estimates of the overall metallicity ( [ Fe/H ] ) of individual Red Giant Branch ( RGB ) stars in two nearby dwarf spheroidal galaxies ( dSphs ) agree to \pm 0.1-0.2 dex with detailed high resolution spectroscopic determinations for the same stars over the range -2.5 < [ Fe/H ] < -0.5 .
For this study we used a sample of 129 stars observed in low and high resolution mode with VLT/FLAMES in the Sculptor and Fornax dSphs .
We also present the data reduction steps we used in our low resolution analysis and show that the typical accuracy of our velocity and CaT [ Fe/H ] measurement is \sim 2 km s ^ { -1 } and 0.1 dex respectively .
We conclude that CaT- [ Fe/H ] relations calibrated on globular clusters can be applied with confidence to RGB stars in composite stellar populations over the range -2.5 < [ Fe/H ] < -0.5 .