I show that the standard microlensing technique to measure the angular radius of a star using color/surface-brightness relations can be inverted, via late-time proper motion measurements, to calibrate these relations. The method is especially useful for very metal-rich stars because such stars are in short supply in the solar neighborhood where other methods are most effective, but very abundant in Galactic bulge microlensing fields. I provide a list of eight spectroscopically identified high-metallicity bulge stars with the requisite finite-source effects, seven of which will be suitable calibrators when the Giant Magellan Telescope comes on line. Many more such sources can be extracted from current and future microlensing surveys.

Abstract
1. INTRODUCTION
2. MICROLENSING AND ANGULAR RADII
3. USING MICROLENSING TO CALIBRATE THE RELATION
    3.1. Uncertainty of θ∗ Measurement
    3.2. Uncertainty of Surface Brightness Measurement
    3.3. Spectra
4. HIGH METALLICITY TARGETS
REFERENCES

• ANDREW GOULD(Department of Astronomy, Ohio State University) CORRESPONDING AUTHOR