Various formulas relate energy delay to group delay. This chapter illuminates those that are one-dimensional. In observational work, it is commonly said that ``what you see is the group velocity.'' This means that when we see an apparently sinusoidal wave train, its distance from the source divided by its traveltime (group delay) is the group velocity. An interesting example of a dispersive wave is given in FGDP (Figure 1-11).