This Project aims to rectify one of the most fundamental and all-pervasive problems in models of stars: how to locate the boundaries of convection. It intends to do this by calculating the highest-resolution 3D simulations of stars in the world and making cutting-edge observations of star clusters. The impact of this advance on stellar modelling would be profound since almost all stars contain convective regions. Many branches of astronomy rely on stellar models so the impact would extend far beyond the immediate field, ultimately expanding our understanding of the Universe. It would also be crucial in realising the scientific advances of the revolutionary new surveys which are right now gathering exquisite data for up to a billion stars.