Scientists at the National Institute of Standards and Technology, or NIST, are developing atomic clocks that are so accurate that the effects of the general theory of relativity come into play. That means if two of these clocks are at slightly different elevations—even a few centimeters—the higher clock runs noticeably faster. In this episode, find out why this is a problem for NIST, how the National Geodetic Survey helped to solve this problem, and how these amazing atomic clocks may someday play an important role in the science of geodesy.