In Time transfer, one of the primary goals is to compare clocks and/or frequency standards over widely separated distances. There are many reasons for making such comparisons. One can simply be interested in making instantaneous measurements of widely separated clocks to monitor the performance of time scales through the intermediary of the clocks being compared. One can also be interested in making comparisons of advanced frequency standards, such as cesium fountains, and/or checking the long-term stability of such standards. The precision and accuracy with which these measurements can be achieved is of interest for metrology.