deletions | additions       diff --git a/Concepts.tex b/Concepts.tex  index f19001f..286da0d 100644  --- a/Concepts.tex  +++ b/Concepts.tex 
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\label{sec:ph_streams}  The fundamental data at the core of smFRET experiments is the array of photon  arrival timestamps, with a temporal resolution usually  of the order of 10~ns. In single-spot measurements, all the timestamps are stored in a single array. In multi-spot  measurements~\cite{Ingargiola_2013} we have as many timestamps arrays as the number of excitation  spots. 
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An estimation of the background rates is needed both to select a proper threshold for  burst search and to correct the raw burst counts by subtracting the background counts.  Furthermore, it is advisable to periodially periodically  estimate the background in order to track occasional variations during the measurement. Experimentally  we found that when the background is not constant, it varies on time scales of tens of seconds   (see figure~\ref{fig:bg_timetrace}). FRETBursts splits the data in uniform time 
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\href{http://fretbursts.readthedocs.org/en/latest/plots.html}{built-in plot functions}  for \verb|Data| objects.   The plot syntax is the same both for single and multi-spot measurements.   Almost all the The majority of  plot commands are called through the wrapper function \verb|dplot|, for example to plot a timetrace of the photon data we type:  \begin{verbatim}