GPS, GLONASS, Galileo, BeiDou (Global Navigational Satellite Systems, GNSS) are miracles of engineering. And within any complex system hide surprises and unsuspected complications. In this post I go over how we resolved an odd observation: that everyone (including major institutions) reported that one of the Galileo satellites (E24) appeared to be off by 1.5 meters, while actual positioning equipment (like phones) showed no problems at all. Through the explanation, we’ll casually learn a thing or two about the cool concept of multi-frequency GNSS.