void Zoom(TObject *o)
{
   static TObject *prev = 0;
   static TCanvas *c = 0;
   TObject *mem = o;
   TString nname;

   if (o->InheritsFrom(TKey::Class())) {
      mem = ((TKey*)o)->ReadObj();
      // prevent memory leak
      if (prev) delete prev;
   }
   if (c) delete c;

   if (mem->InheritsFrom(TH2::Class())) {
      TH2 *hist = (TH2*)mem;
      // set colz
      hist->SetOption("colz");

      // zoom hist
      hist->SetAxisRange(-2,2,"X");
      hist->SetAxisRange(-2,2,"Y");
      if (mem==o) return;  //  hist in memory

      // hist from file
      hist->SetDirectory(0);      
      nname = hist->GetName();
      nname += "_colz";

      // change hist name to prevent deletion
      hist->SetName(nname);

      c = new TCanvas("c1","hist canvas",400,800);
      c->Divide(1,2);
      c->cd(1);
      hist->Draw();
      c->cd(2);
   }
}