Unsigned active region magnetic flux (solid black curve) and critical height (dashed blue curve) in HARP 5880 against time. Initially, the magnetic flux decreases and the critical height increases (phase shaded in pink), then magnetic flux begins to increase and the critical height falls (shaded orange). As flux emergence continues, the critical height increases once more (shaded purple). The onset time of the CME observed in this region is given by the vertical black line.