Placed here in 1850, this granite monument marks the western end of the Edisto baseline, whose matching monument still stands 6.68 miles to the east. These monuments are among the few surviving end-point monuments of the seven baselines measured by the U.S. Coast Survey from the 1830s through the 1850s. Edisto's baseline was the third critical line that Professor Bache measured between Maine and the Gulf of Mexico, and when this monument was rediscovered, it was the oldest Bache line still intact. To test the accuracy of Bache's measurement, mappers in the 1990s re-surveyed the line using America's $10-billion Global Positioning System. What Bache's team had worked on for weeks, GPS measured in one hour, yet the difference in speed did not produce a difference in accuracy: the Bar of Invariable Length had produced a line less than 2.5 inches from perfection over a nearly 7-mile length. Before its 1850 installation, this granite monument was stamped and brought by sailing ship from New England.