  The simplified scaling of the orbital upper critical field, $H_{c2}(T)$, for
the isotropic case is discussed. To facilitate the analysis of the experimental
data, we suggest a simple but accurate approximation in the entire temperature
range of the scaled upper critical field valid for any transport scattering
rate $H_{c2}/H_{c2}(0) \approx (1-t^2)/(1+0.42 \,t^{1.47})$.
