Left: Snapshot from a hot spot movie, with resolution 256 × 256 (as in the entire library), where ΔPA is calculated from the primary to the secondary counterclockwise. Middle: Curve of ΔPA measurement with respect to time for a full period. Right: Time lag (difference in arrival times) between the first and second image. The gray vertical line in the right panels denotes the snapshot’s time in the left panels.