Very high astrometric accuracy has multiple uses in astronomy, including discovering and measuring the masses of exoplanets down to Earth mass. In the last year or so, we've undertaken an effort to identify and calibrate the biases in an astrometric telescope. There are two main sources of astrometric bias, the focal plane and the optics. We'll describe progress in focal plane calibration, where we've demonstrated centroiding to 1e-4 pixels (goal is 1e-5 pixels) by measuring the precise location of each pixel as well the intrapixel QE variations. Calibration of the optical distortion of a telescope is an activity that we're just starting, but the concept is based on a diffractive optic at the pupil of the telescope. Last of all I'll describe plans to demonstrate these concepts on a small telescope at JPL's table mountain. The objective for accurate absolute ground based astrometry (relative to GAIA stars) is to enable ground based optical navigation of future laser bearing spacecraft, at a precision similar to radio navigation.