  The threshold scan at future lepton colliders is the most precise known
method to determine the top quark mass (well below 100 MeV), a fundamental
parameter of the Standard Model that co-determines the stability properties of
the electroweak vacuum. We present a new method to match the continuum
next-to-leading order QCD corrections with the next-to-leading logarithmic
resummation of the Coulomb singularities of the quasi-toponium bound state at
threshold where fixed-order perturbation theory is invalid. This matching is
performed at the level of the fully exclusive $W^+bW^-\bar{b}$ final state. It
allows to study all kinds of differential distributions at or close to
threshold. The top mass dependence of these distributions opens up new
possibilities for the top mass determination that might be competitive with the
inclusive threshold scan.
