uncertainty propagation

[fgnievinski]

early versions of the IEEE preprint included a derivation of the propagation of uncertainty, from input $N$ and $\delta e$ ($\sigma_N$ and $\sigma_{\delta e}$), into output, $d$ and $\Delta H$ ($\sigma_d$ and $\sigma_{\Delta H}$). it might be worthwhile to revisit that in a separate paper.