The ITRF96 height difference between the VLBI and GPS positions at Westford is approximately three centimeters different from the eccentricity, after the IERS eccentricity has been corrected for a numerical error (memo by W. Strange, 1996). This eccentricity is based on GPS measurements. An optical survey in 1996, having an accuracy of about 5 mm, agrees with the corrected eccentricity to one centimeter. In order to check the GPS component of the eccentricity a Dorne-Margolin choke- ring (DMCR) antenna was mounted on a tripod over the reference mark nearest the VLBI antenna. While the DMCR to DMCR height for a minimum elevation of 15 degrees agrees with the optical measurement, the height difference has a sensitivity of approximately -3 mm per degree of minimum elevation. The sensitivity of height to minimum elevation was evaluated for all of the antennas used in the orbit/clock solution for one day. The 5 degree to 30 degree difference ranged from about +1 to -10 cm. Thus the Westford height discrepancy may be due to the distribution of height errors averaged over the global network.