Upper panel: galactic GC fiducials from DA90 shown as black dashed lines, along with Dartmouth isochrones shown as red solid lines. From left to right, the Galactic GC fiducials correspond to M 15, NGC 6397, M 2 and 47 Tuc, where the GCs have a metallicity of  −2.17,  −1.91,  −1.58 and  −0.71 dex, respectively, on the ZW84 scale. The isochrones correspond to an age of 12.5 Gyr and have the same metallicities as the Galactic GCs, from left to right. Middle panel: analytic functions of Galactic GC fiducial loci from Saviane et al. (2000a) on the ZW84 scale (black dashed lines) along with Dartmouth isochrones of 12.5 Gyr (red solid lines). The metallicities correspond to  −1.99,  −1.37,  −1.23,  −1.15, and  − 0.7 dex from left to right, respectively. Lower panel: the same as in the middle panel but for the CG97 metallicity scale. The metallicities correspond to  −2.11,  −1.67,  −1.53,  −1.33, and  −0.71 dex from left to right, respectively.