Not yet reviewed by Pith; the record is open.

Massive star evolution is dominated by key physical processes such as mass loss, convection and rotation, yet these effects are poorly constrained, even on the main sequence. We utilise a detached, eclipsing binary HD166734 as a testbed for single star evolution to calibrate new MESA stellar evolution grids. We introduce a novel method of comparing theoretical models with observations in the 'Mass-Luminosity Plane', as an equivalent to the HRD (see Higgins & Vink, 2018). We reproduce stellar parameters and abundances of HD166734 with enhanced overshooting (alpha=0.5), mass loss and rotational mixing. When comparing the constraints of our testbed to the systematic grid of models we find that a higher value of alpha = 0.5 (rather than 0.1) results in a solution which is more likely to evolve to a neutron star than a black hole, due to a lower value of the compactness parameter.