PM errors in the right ascension and declination components as found combining two HST epochs (black dots) or the corrected GeMS images with the first epoch of HST data (red dots). Cyan lines describe the 3σ-clipped mean trends in the two cases (continuous and dashed lines corresponding to the HST-HST and the HST-GeMS cases, respectively). From the comparison it is evident that the performance is similar until m_F555W ≃ 21.5 mag, where our new PM precision becomes approximately a factor of two larger than that coming from HST.