deletions | additions       diff --git a/Concepts.tex b/Concepts.tex  index 4630204..99a64d1 100644  --- a/Concepts.tex  +++ b/Concepts.tex 
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Likelihood Estimation (MLE) or a curve fit of the histogram via non-linear  least squares (NLSQ) must be selected.  It is advisable to check the background a at  different time points throughout the measurements in order to track occasional variations.  Experimentally we found that when the background is not constant,  it usually varies 
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during acceptor excitation period (present only in ALEX measurements)  \end{itemize}  The previous fields are always background-corrected. background-corrected by default.  Furthermore, \verb|na| is corrected for leakage and direct excitation if the  relative coefficients are specified (by default they are 0).