Comparison of relative proper motion versus the magnitude of the semi-major axis of the error ellipse of the proper motion for all 193 O-stars in our core sample, with the filled symbols representing those stars with errors less than 0.07 mas yr⁻¹ in both proper motion ordinates. Ignoring outliers, it is apparent that the dispersion of proper motions begins to increase significantly above 0.07 mas yr⁻¹ (vertical dashed line). For illustration the horizontal dashed line represents a velocity of 50 km s⁻¹ at the distance of the LMC. Labels are the VFTS identification numbers for those stars discussed in the text.