void afzaal() {
   TFile f1 = TFile::Open("aluminium.root", "READ");
   h1->SetLineWidth(2);
   h1->SetLineColor(kBlack);
   h1->SetMarkerColor(kBlack);
   h1->SetMarkerStyle(2);
   h1->Draw("hist");

   TFile f2 = TFile::Open("glass.root", "READ");
   h1->SetLineWidth(2);
   h1->SetLineColor(kRed);
   h1->SetMarkerColor(kRed);
   h1->SetMarkerStyle(2);
   h1->Draw("hist same");

   TFile f3 = TFile::Open("bakelite.root", "READ");
   h1->SetLineWidth(2);
   h1->SetLineColor(kGreen);
   h1->SetMarkerColor(kGreen);
   h1->SetMarkerStyle(2);
   h1->Draw("hist same");

   TH1 h_first = static_cast<TH1>(f1->Get("h1"));
   TH1 h_second = static_cast<TH1*>(f2->Get("h1"));
   TH1* h_third = static_cast<TH1*>(f3->Get("h1"));

   auto legend = new TLegend(0.1,0.7,0.48,0.9);
   legend->AddEntry(h_first, "aluminium");
   legend->AddEntry(h_second, "glass");
   legend->AddEntry(h_third, "bakelite");
   legend->Draw();

   Double_t scale=1./h1->Integral();
   h1->Scale(1/h1->Integral());
   h1->Draw("hist same");
}