  The MINOS experiment has observed a rise in the underground muon charge ratio
$r_\mu$ = ${\mu^+/\mu^-}$. This ratio can be related to the atmospheric
production ratios of ${\pi^+/\pi^-}$ and ${K^+/K^-}$. Our analysis indicates
that the relevant variable for studying the charge ratio+ $\ecos$, rather than
$\emu$. We compare a simple energy dependent parameterization of the rise in
the charge ratio with more detailed previously published Monte Carlo
simulations and an analytical calculation. We also estimate the size of two
previously neglected effects in this context: the charge sign dependency of the
dE/dx in rock, and the energy dependence of heavy primaries on the derived
${K^+/K^-}$ ratio.
