Top: Hα (black) and Hβ (red) V/R curves. Three complete V/R cycles were covered between 1997 and 2010. The gray regions indicate the triple-peak phase for each cycle. Bottom: measured quantities illustrated on a Hβ line profile: violet (AA′) and red (BB′) emission peaks, depth of the central absorption (CC′) and asymmetry (FG/FH ratio). The respective radial velocities of the three components (emission peaks and central absorption) were measured whenever possible. The horizontal line marks the normalized continuum.