void Second_x_axis() {
    auto canv = new TCanvas("s1","second axis"); 
    
    canv->SetLogy();

    Double_t nBins = 200000;
    Double_t endPoint = 800000;
    Double_t beginPoint = 0;

    TFile *f1 = TFile::Open("data.root");
    TH1D *h1 = new TH1D("sim1", "current", nBins, beginPoint, endPoint);
    TTreeReader myReader1("DataTree", f1);
    TTreeReaderValue<Double_t> myInjEnergy1(myReader1, "TRAP2");
    while (myReader1.Next()) { h1->Fill(*myInjEnergy1);}	
    h1->Draw("HIST L SAME");
    h1->SetLineColor(kBlack);

    Double_t p_0 = 1.21545e-02;  Double_t p_1 = 6.48653e-05;  // 04-03-2024

    auto low_bin = h1->GetXaxis()->GetXmin();
    auto up_bin = h1->GetXaxis()->GetXmax();
    h1->SetTitle("");
    
    h1->GetXaxis()->Set(nBins, low_bin*p_1+p_0, up_bin*p_1+p_0); //calibrating the x-axis
    TF1 *func = new TF1("func","(x - [0])/[1]",0,endPoint); //reverse calibration to get the bin numbers again.
    func->SetParameters(p_0,p_1);
    TGaxis *axis = new TGaxis(gPad->GetUxmin() ,gPad->GetUymax(), gPad->GetUxmax(), gPad->GetUymax(),beginPoint ,endPoint, 10, "-"); //drawing the Gaxis using the user coordinates
    axis->Draw("same");
    axis->SetTitle("Channels");
    axis->CenterTitle(true);

    h1->SetStats(0);
    h1->GetXaxis()->SetTitle("Energy [MeV]");
    h1->GetXaxis()->CenterTitle(true);
    h1->GetYaxis()->SetTitle("Counts");
    h1->GetYaxis()->CenterTitle(true);

    canv->Update();
}