  We analyze the Sudbury Neutrino Observatory (SNO) and Super-Kamiokande (SK)
data on charged current (CC), neutral current (NC) and neutrino electron
elastic scattering (ES) reactions to constrain the leading weak axial two-body
current parameterized by L_1A. This two-body current is the dominant
uncertainty of every low energy weak interaction deuteron breakup process,
including SNO's CC and NC reactions. Our method shows that the theoretical
inputs to SNO's determination of the CC and NC fluxes can be self-calibrated,
be calibrated by SK, or be calibrated by reactor data. The only assumption made
is that the total flux of active neutrinos has the standard ^8B spectral shape
(but distortions in the electron neutrino spectrum are allowed). We show that
SNO's conclusion about the inconsistency of the no-flavor-conversion hypothesis
does not contain significant theoretical uncertainty, and we determine the
magnitude of the active solar neutrino flux.
