  The top-quark mass can be determined with very high precision from a scan of
the total $e^+e^-\to b\bar{b}W^+W^-X$ cross section near the top-pair
production threshold. We present the full calculation of electroweak and
non-resonant corrections to this process at NNLO. We discuss the size of the
new contributions and estimate the theory uncertainty on the top-quark mass in
the PS mass scheme.
