  A method to facilitate the consistent inclusion of cross-section measurements
in proton parton density functions (PDFs) fits in NLO QCD has been developed.
It allows the a posteriori variation of the renormalisation and factorisation
scales and of the centre-of-mass energy and the inclusion of arbitrary PDFs,
strong coupling in cross-section calculations. The theoretical uncertainties in
the double differential single inclusive jet cross-section at a $\sqrt{s}=7$
TeV have been studied using this method.
