\section{Introduction}

As others have recognized in the past\cite{numi-b-781} the spectra at
near (ND) and far (FD) detectors in a long baseline neutrino
oscilation experiment are highly corelated.  This is due to the fact
that the neutrinos come from the same hadron decays.  In reference
\cite{numi-b-781} a method to exploit this is given.  This note
expands on that method by providing the formalism.  This formalism
will show that the method as previously understood is subtly, and
slightly incorrect.  This formalism is given in
section\ref{sec:formal}.

Section \ref{sec:compare} shows comparisons with other methods.

Finally, section \ref{sec:systematics} discusses some of the
systematics that remain with this method.

%%% Local Variables: 
%%% mode: latex
%%% TeX-master: "main"
%%% End: