  The scaling properties of the conductance of a Kondo impurity connected to
two leads that are in or out of equilibrium has been extensively studied, both
experimentally and theoretically. From these studies, a consensus has emerged
regarding the analytic expression of the scaling function. The question
addressed in this brief report concerns the properties of the experimentally
measurable coefficient $\alpha$ present in the term describing the leading
dependence of the conductance on $eV/T_K$, where $V$ is the source-drain
voltage and $T_K$ the Kondo temperature. We study the dependence of $\alpha$ on
the ratio of the lead-dot couplings for the particle-hole symmetric Anderson
model and find that this dependence disappears in the strong coupling Kondo
regime in which the charge fluctuations of the impurity vanish.
