Dependence, for HIP 57367 (see Table 4), of σ_vr (required to reach c_robust = 68.27%) and the robust confidence level c_robust on the Factor of Safety (FoS), i.e., the minimum factor between the predicted HTPM standard error and the perspective-acceleration-induced HTPM proper-motion error caused by radial-velocity errors. The default FoS value adopted in this study is 10. The object is representative for a nearby star with a well-determined parallax. The straight, red lines indicate linear scaling relations starting from the default value FoS = 10.