A geodetic datum based on the Mercury ellipsoid 1960 and located with respect to a number of major datums of the world by a large, given set of constants. It was used principally by the USA in computing orbits and trajectories from observations made at tracking stations on that datum, in particular, those tracking stations used in Project Mercury. It has also been used as the datum for locating OMEGA, LORAN-C and LORAN-A stations.