In this paper we briefly outline the quadrature method for estimating
uncertainties in a function of several variables and apply it to estimate the
numerical uncertainties in QCD-QED rescaling factors. We employ here the
one-loop order in QED and three-loop order in QCD evolution equations of
fermion mass renormalization. Our present calculations are found to be new and
also reliable compared to the earlier values employed by various authors.Comment: 14 page