Usage of  NTUPLE/HMERGE
                                                                                   
      opt stat                                                                                                          
1     HMERGE CWN_APTUPLE_MERGE.HBOOK CWN_APTUPLE.HBOOK CWN_APTUPLE.HBOOK                                         
      HI/FILE 1 CWN_APTUPLE_MERGE.HBOOK                                                                                 
2     NT/PLOT 11.AGE                                                                                             

1. The command HMERGE merge HBOOK files containing histograms and/or ntuples. Ntuples are merged and histograms with the same identifier are added.
2. As we can see in the statistics box, the new Ntuple has now the double of entries.