Comparison between the east and west halves of the ER. Top: evolution of the east-west flux density ratio over time in each band. The clearest change occurs between 2006 and 2010. Bottom: light curves of the east (open symbols and dashed lines) and west (solid symbols and lines) halves. The strongest difference in evolution again occurs between 2006 and 2010, and mainly in the west. Afterward, the evolution is similar in both halves.