Simulated astrometric track for the GaiaDR3-ULENS-001 event. The solid blue line marks the source path without the microlensing effect. The thin, dashed black line marks the light centroid path. The coloured dots mark the light centroid positions during the measurement epochs per CCD. The thick, dashed black line shows the path corresponding to the five-parameter fit obtained by Gaia. The light grey lines represent randomly selected MCMC samples. The simulated track for the negative u₀ solution is very close and was omitted for clarity.