We study the melting of quasi-two-dimensional colloidal hard spheres by considering a tilted monolayer of particles in sedimentation-diffusion equilibrium. In particular, we measure the hard-disk equation of state from the density profiles and use time-dependent and height-resolved correlation functions to identify the liquid, hexatic and crystal phases. We find that the liquid-hexatic transition is first order and that the hexatic-crystal transition is continuous. Furthermore, we directly measure the width of the liquid-hexatic coexistence gap from the uctuations of the corresponding interface, and thereby experimentally establish the full phase behaviour of hard disks
