  We present a method to establish experimentally the relation between the
top-quark mass $m_t^{MC}$ as implemented in Monte-Carlo generators and the
Lagrangian mass parameter $m_t$ in a theoretically well-defined renormalization
scheme. We propose a simultaneous fit of $m_t^{MC}$ and an observable sensitive
to $m_t$, which does not rely on any prior assumptions about the relation
between $m_t$ and $m_t^{MC}$. The measured observable is independent of
$m_t^{MC}$ and can be used subsequently for a determination of $m_t$. The
analysis strategy is illustrated with examples for the extraction of $m_t$ from
inclusive and differential cross sections for hadro-production of top-quarks.
