Double_t GetMean(Int_t axis = 1) const
For axis = 1,2 or 3 returns the mean value of the histogram along
X,Y or Z axis.
For axis = 11, 12, 13 returns the standard error of the mean value
of the histogram along X, Y or Z axis
Note that the mean value/RMS is computed using the bins in the currently
defined range (see TAxis::SetRange). By default the range includes
all bins from 1 to nbins included, excluding underflows and overflows.
To force the underflows and overflows in the computation, one must
call the static function TH1::StatOverflows(kTRUE) before filling
the histogram.