Detection of earth-size exoplanets using the astrometric signal of the host star requires sub microarcsecond measurement precision. One major challenge in achieving this precision using a medium-size (<2-m) space telescope is the calibration of dynamic distortions. The researchers propose a diffractive pupil technique that uses an array of approximately 50um dots on the primary mirror that generate polychromatic diffraction spikes in the focal plane. The diffraction spikes encode optical distortions in the optical system and may be used to calibrate astrometric measurements. This concept can be used simultaneously with coronagraphy for exhaustive characterization of exoplanets (mass, spectra, orbit). At the University of Arizona, a high precision astrometry laboratory is being developed to demonstrate the capabilities of this diffractive pupil concept. The researchers aim to achieve 10 μas single-axis precision in the laboratory, simulating 0.14 μas precision on a 1.4 m space telescope. This paper describes this laboratory and presents the data and results obtained so far.