histograms "passed" and "total" have
to fullfill the conditions  mentioned in <a
    href="http://root.cern.ch/root/html/TEfficiency.html#TEfficiency:CheckConsistency">CheckConsistency</a>,
    otherwise the construction will fail.
    <li>Example 2: Create TEfficiency from 2 existing histograms:
    <pre>
TEfficiency * pEff = 0;
if (TEfficiency::CheckConsistency(h_pass,h_total))
   pEff = new TEfficiency(h_pass,h_total);
   </pre>
    </li>
</ul>
  </li>

<li>
   The TEfficiency class provides various stat