Upper panel: a segment of the A8b series illustrating how HXDs are evaluated in single bursts. Black and red data are the count rate and mean energy series, respectively. The zero level corresponds to the values of the centroid of the ellipse in the CR − E plot. Long and short vertical bars mark the time intervals of HXD₁ and HXD₂, respectively. Lower panel: a segment of equal duration of the F7 series. We note that both HXDs are longer than in the A8b series.