Simulation of an orbital motion as seen by Hipparcos (red dots) and Gaia (DR3; blue dots) around GJ 832 for a companion mass of 100 M_J and sma=1 au, e=0, I_c=0^∘. For visualization, we added a virtual proper motion of 30 mas/yr along the RA direction. The individual astrometric measurements are scattered along the along-scan directions at each FoV transit epoch with σ_AL=0.095 mas and σ_calib=0.15 mas for Gaia and an average dispersion of ∼4.2 mas for Hipparcos. The orange and cyan crosses respectively mark the position of the fit centroid on the Hipparcos and Gaia datasets.