{
  TFile file("BFBMvec.root");
  // this file has an ntuple named "field"

  TCanvas* c = new TCanvas("c", "Bz v. Z for varying Y", 0, 0, 800, 600 );
  c->SetFillColor(19);
  field->SetMarkerStyle(6);
  field->SetMarkerColor(kGreen);
  field->Draw("bz:z","x==-3904 && y==0");
  field->SetMarkerColor(kCyan);
  field->Draw("bz:z","x==-3904 && y==300","same");
  field->SetMarkerColor(kViolet);
  field->Draw("bz:z","x==-3904 && y==600","same");
  field->SetMarkerColor(kMagenta);
  field->Draw("bz:z","x==-3904 && y==800","same");
  field->SetMarkerColor(kOrange);
  field->Draw("bz:z","x==-3904 && y==940","same");
  leg = new TLegend(0.5,0.2,0.8,0.4,"X = -3904mm, Y = :");
  leg->AddEntry(field,"0 mm (center)", "p");
  leg->AddEntry(field,"300 mm", "p");
  leg->AddEntry(field,"600 mm", "p");
  leg->AddEntry(field,"800 mm", "p");
  leg->AddEntry(field,"940 mm", "p");
  leg->Draw();
  htemp->SetTitle("Bz v. Z at X=-3904mm for various Y");
  c.Update();

}