{
   TCanvas *canvas = new TCanvas("canvas","canvas");
   TTree *tree = new TTree ("tree","tree");
   tree->ReadFile("boog.dat","source/C:HV:HV_err:R:R_err");

   Int_t N = tree->Draw("HV:R:HV_err:R_err","","goff");

   TGraphErrors *gr = new TGraphErrors(N,
                                       tree->GetV1(),
                                       tree->GetV2(),
                                       tree->GetV3(),
                                       tree->GetV4());
   gr->Draw("AP");
}