The PM vectors from Gaia DR2 (red) and this study using HST + Keck (HK; blue) show good agreement. In this figure, the bulk motion of the ONC inferred from the median values of the difference between the absolute and relative PMs (﹩\widetilde{{\rm{\Delta }}{\mu }_{{\alpha }^{* }}}﹩, ﹩\widetilde{{\rm{\Delta }}{\mu }_{\delta }}﹩) = (1.6, 0.6) mas yr⁻¹ was subtracted from those from Gaia DR2 (see Figure 3). Gray dots illustrate the positions of all stars in our sample.