In July 2003, NOAA's National Geodetic Survey (NGS) began a research project in North Carolina to test how much data surveyors need to meet accuracy standards. NGS contracted with Dewberry and Davis (D&D) to set up a test network of 25 stations around Raleigh, observe them for four days, and compute coordinates from the data. Using the computations as truth, NGS and D&D are performing tests using segments of the data extracted from the full dataset to determine how much data is necessary to achieve an accuracy of 2 cm in the vertical component. NGS will use the results to update the Guidelines for Establishing GPS-Derived Ellipsoid Heights, NOS NGS-58. For more information, please contact Joe Evjen.