Lens system configuration of KMT-2021-BLG-0284. The red figures composed of concave curves represents the caustic. The two black filled dots indicate the positions of the lens components; the bigger one represents the heavier component. The black and blue arrowed lines represent the trajectories of the primary (S₁) and secondary (S₂) source stars, respectively. The arrow tips on the trajectories are shown at the same moment in time. The points marked as t₁, t₂, t₃, and t₄ on the source trajectories represent the source positions at the times of the anomalies marked in Fig. 1. Gray curves encompassing the caustic are equi-magnification contours.