Estimates of the atmospheric parameters for the targets from the VFTS (upper) and FLAMES-I survey (lower); some targets have been moved slightly in effective temperature to improve clarity. Targets with an estimated nitrogen abundance, 7.2 ≤ϵ_N < 7.5 dex, are shown as asterisks and those with ϵ_N ≥ 7.5 dex are shown as triangles; all other targets are shown as crosses. Evolutionary models of Brott et al. (2011a; solid black lines) and Georgy et al. (2013b; solid red lines) are shown for zero initial rotational velocity together with the initial mass (in units of the solar mass). Isochrones (dashed lines) are shown as dotted lines with the same colour selection for ages of 5, 10, and 20 Myr. Typical uncertainties in the effective temperatures and gravity estimates are also shown.