  The experimental systematic uncertainties associated to the reconstruction
and calibration of the objects appearing in top quark final states at the LHC
and Tevatron are discussed. The strategies followed in the ATLAS and CMS
experiments are compared in detail for the cases of the jet energy scale and
$b$-tagging calibrations, where a categorisation of the associated uncertainty
sources as well as the corresponding correlations across experiments has been
proposed. The estimate of the non-prompt and fake lepton background to the top
quark leptonic channels is also discussed.
