Relative a posteriori corrected PMs, $\mathrm{\Delta }{\mu }_{\alpha }\cos \delta$ and Δμ_δ, of well-measured NGC 1850 member stars as a function of the m_F814W magnitude (left panels) and the m_F438W − m_F814W colour (right panels). The orange points are median values within bins containing approximately equal numbers of objects (edges of the bins are indicated as grey vertical lines). Error bars, calculated as the standard error of the mean, are also shown but are generally smaller than the shown points. The horizontal grey line in each panel is set at Δμ = 0.0 mas yr⁻¹.