void vdct0plane(int runnumber,int cal=0,int out=0){
  //extract from rawtdc

 //  char root_dir[300] = "$ROOTFILES/2011-08-18/vdct0";
//   TFile *file = new TFile(Form("%s/e07006_vdct0_%d.root",root_dir,runnumber));

  char root_dir[300] = "/taidisk/L_det";
  TFile *file = new TFile(Form("%s/e07006_L_det_%d.root",root_dir,runnumber));

  TTree *T = (TTree*)file->Get("T");
  cout<<"run "<<runnumber<<" with entries "<< T->GetEntries()<<endl;

  int const offsetCh = 1800;
  int const NBIN= 175;
  int const DOM_MIN = 0;
  int const DOM_MAX = 700;
  double binwidth = (DOM_MAX-DOM_MIN)/NBIN;


  int const ARM=1;
  int const PLANE=4;
  char arm[ARM][10] = {"L"}; //{"L","R"};
  char plane[PLANE][100] = {"u1","v1","u2","v2"};

  TH1F *hist[ARM][PLANE];
  char hist_name[ARM][PLANE][300];
  char plot_var[ARM][PLANE][300];
  char plot_hist[ARM][PLANE][300];
  char select[300] = "";
  // char select[300] = "DBB.evtypebits&(1<<3)";


  TLine *bmax[ARM][PLANE];
  TLine *zero[ARM][PLANE];
  double offset[ARM][PLANE];


  for(int i=0;i<ARM;i++){
    for(int j=0;j<PLANE;j++){
      sprintf(plot_var[i][j],"%d-%s.vdc.%s.rawtime",offsetCh,arm[i],plane[j]);
      sprintf(hist_name[i][j],"%s_%s_tdc_value",arm[i],plane[j]);
      hist[i][j] = new TH1F(hist_name[i][j],hist_name[i][j],NBIN,DOM_MIN,DOM_MAX);
      hist[i][j]->GetXaxis()->SetTitle("TDC channel");
      sprintf(plot_hist[i][j],"%s>>%s",plot_var[i][j],hist_name[i][j]);
    }
  }


  int binmax,currentbin;
  double binmaxvalue,binmaxedge,halfbinwidth;
  double x_maxslope;
  double slope, maxslope;
  //double aver=0;

  
  //TCanvas *vdc = new TCanvas("vdc","vdc: t0 ",800,600);
  TCanvas *vdc = new TCanvas("vdc",Form("vdc: t0 : run %d",runnumber),800,600);
  vdc->Divide(2,4);
  for(int i=0;i<ARM;i++){
    for(int j=0;j<PLANE;j++){
      vdc->cd(i*PLANE+j+1);
      T->Draw(plot_hist[i][j],select);

      if(cal){///////
      //calculate average background
      //maximum bin properties
      binmax = hist[i][j]->GetMaximumBin();
      binmaxvalue = hist[i][j]->GetBinContent(binmax);
      binmaxedge = hist[i][j]->GetBinLowEdge(binmax);
      halfbinwidth = 0.5*(hist[i][j]->GetBinWidth(binmax));
      currentbin = binmax;

      bmax[i][j] = new TLine(binmaxedge+halfbinwidth,0,binmaxedge+halfbinwidth,binmaxvalue);
      bmax[i][j]->SetLineColor(kBlue);
      bmax[i][j]->Draw("same");

      //cout<<"bin max "<< binmax<< "has count "<<binmaxvalue<<" at edge"<<binmaxedge<<endl;
      maxslope = 0;
      for(int k=binmax;k>0;k--){
	slope = hist[i][j]->GetBinContent(k) - hist[i][j]->GetBinContent(k-1);
	if(slope>maxslope){
	  maxslope = slope;
	  x_maxslope = hist[i][j]->GetBinLowEdge(k-1)+0.5*binwidth; 
	}
      }
      offset[i][j] = x_maxslope;
      //cout<<"max change "<< maxslope<<" at value " << x_maxslope<<endl;
      zero[i][j] = new TLine(offset[i][j],0,offset[i][j],binmaxvalue);
      zero[i][j]->SetLineColor(kRed);
      zero[i][j]->Draw("same");

      TLatex *txt = new TLatex();txt->SetNDC(); txt->SetTextSize(0.11); txt->SetTextColor(kRed);
      char txtstring[300];
      sprintf(txtstring,"adjust t_{0} to channel %4.1lf ",offsetCh-offset[i][j]);
      txt->DrawLatex(0.5,0.7,txtstring);
      }/////////if
      vdc->Update();

    }
  }  
  //vdc->Print(Form("/home/nmuangma/2011SRC/scripts/vdc_calibration/time_plots/tdc_%d.png",runnumber));
 
  if(out){
    //vdc->Print(Form("/home/nmuangma/2011SRC/scripts/vdc_calibration/time_plots/tdc_%d.png",runnumber));
  //vdc->Print("./time_plots/t0_vdc_fromlist.png");

  FILE *fw = fopen("/home/nmuangma/2011SRC/scripts/vdc_calibration/tdclist20110621.dat","a");
  fprintf(fw,"run %4d   ",runnumber);
  fprintf(fw,"entries %7d  ",T->GetEntries());
  for(int i=0;i<ARM;i++){
    for(int j=0;j<PLANE;j++){
      fprintf(fw,"%s_%s %4.1lf   ",arm[i],plane[j],offsetCh-offset[i][j]);  
    }
  }
  fprintf(fw,"\n");
  fclose(fw);
  }
}