void ZOffset3D( TH3* h, float z) {
//     This boosts the height for each bin of a histogram by a given constant value of z
   int nbinx = h->GetNbinsX();
   int nbiny = h->GetNbinsY();
   int nbinz = h->GetNbinsZ();
   for (int i=1; i<=nbinx; i++) {
      for (int j=1; j<=nbiny; j++) {
          for (int k=1; k<=nbinz; k++) {
            h->SetBinContent(i,j,k,z+(h->GetBinContent(i,j,k)) );
          }
      }
   }
}