  We compare several different calculations of the atmospheric neutrino flux in
the energy range relevant for contained neutrino interactions, and we identify
the major sources of difference among the calculations. We find nothing that
would affect the predicted ratio of $\nu_e/\nu_\mu$, which is nearly the same
in all calculations. Significant differences in normalization arise primarily
from different treatment of pion production by interactions of protons in the
atmosphere. Different assumptions about the primary spectrum and treatment of
the geomagnetic field are also of some importance.
