This technical report describes the round robin measurement results for the group delay ripple (GDR) of tunable dispersion compensators (TDCs). It briefly explains the four typical TDCs measured and four typical methods of measuring group delay (GD), as well as the GDR round robin measurement results of TDCs, and an analysis of repeatability and differences among these measurement methods. This technical report also proposes suitable measurement parameters and a new parameter of phase ripple instead of GDR.