  Future high-energy $e^+e^-$ colliders will provide some of the most precise
tests of the Standard Model. Statistical uncertainties are expected to improve
by orders of magnitude over current measurements. This provides a new challenge
in accurately assessing and minimizing systematic uncertainties. Beam
polarisation may hold a unique potential to isolate and determine the size of
systematic effects. This study aims to set this hypothesis by setting up a
combined fit of systematic effect and electroweak observables that can test
different configurations of available beam polarisations and luminosities. A
framework for this fit is developed. In a first test it fits the luminosity and
polarisation with external constraints to 2-fermion and 4-fermion differential
distributions. An implementation of a first systematic - the muon acceptance -
shows consistent behaviour in this framework. This lays the groundwork for
testing the interplay of systematic and physical effects in the presence or
absence of beam polarisation.
