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 5um 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 was developed to demonstrate the capabilities of this diffractive pupil concept. The researchers aim to demonstrate that the diffractive pupil can improve current limiting factors of astrometric accuracy. This paper describes this laboratory and the results showing that this technique can effectively calibrate dynamic distortions.