Flow chart of our procedure to simulate multi-band microlensing curves and how to analyze them. The top row shows how we simulated our “observed data” given a fiducial source, the magnification pattern, and microlensing magnification, μ = −4.28. The negative magnification indicates that the image is at the saddle point. The “template magnification map” used to analyze the data is shown in the middle panel (see text), where preselected locations used in fitting the source size are shown in yellow. These correspond to areas where the microlensing magnification matches the fiducial one with ≤25% error. In the end, we only kept the regions where fitting the source size gives χ² < 1. These are shown in green and were used to produce the distribution of measured source size R_λ0 in the bottom row. For reference purposes, we provide the true (fiducial) size as a red vertical line.