Code for "Plotting the Differences Between Data and Expectation"
  by Georgios Choudalakis and Diego Casadei
  Eur. Phys. J. Plus 127 (2012) 25 
  http://dx.doi.org/10.1140/epjp/i2012-12025-y
  (http://arxiv.org/abs/1111.2062)

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  This code is covered by the GNU General Public License:
  http://www.gnu.org/licenses/gpl.html
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  Quick start: install ROOT from http://root.cern.ch/ and call the
  example script from your command line:

  [prompt]$ root -q -b plotSign.C+

  This will produce the last figure in the paper, showing the
  comparison between data and expectation with an inset plotting the
  bin significance computed from the number of observed events and the
  expected number of events, with and without uncertainty on the
  expectation.

  The math is implemented in pValuePoissonError.C while the ROOT
  graphics is implemented in CompareHistograms.C (both included by
  plotSign.C).  The script plotSign.C is just an example which shows
  how to use these two macros.  In CmpDataMC.C a more elaborate
  example is provided, which also plots a stacked sum of histograms
  representing all contributions to the total expectation.

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  The repository can be accessed as

  Git: (recommended)
     https://github.com/dcasadei/psde

  SVN: (old)
     svn co https://svn.cern.ch/guest/psde 
     svn co svn+ssh://svn.cern.ch/guest/psde