The GMT test has sensitivity to angle of 1.6 µm/µrad or7.9 µm/arcseconds at the outer edge of the mirror, with an average sensitivity to angle of 5.6 µm/arcseconds. This is likely to be a significant source of error in the measurement. When it is combined with increased relative motion of the mirror and tracker over the 22 m separation, we would anticipate an accuracy of 5-10 µm rms without the enhancements of the Laser Tracker Plus system