Histograms of the tilt angles of groups with area weighted centres within 60° central meridian distance. Open bars: entire set, filled bars: groups with a minimum polarity separation of Δβ_min = 3°, and hatched bars: groups with Δβ_min = 3° and a removal of evolutionary outliers that occur in the sequence of tilt angles during the evolution of any given group. This hatched histogram is an attempt to further reduce the influence of occasional unipolar instances of otherwise bipolar groups. See text for the detailed algorithm. The bin width is .