Graphical operations on histograms (Keep and Add)
                                                         
      histogram/file 45 pawhists.hbook                                                                                  
      zone 1 2                                                                                                          
      set htyp 245                                                                                                      
1     H/PL 120 K                                                                                                 
      set htyp 254                                                                                                      
1     H/PL 110                                                                                                   
      set htyp                                                                                                          
2     H/PL 110 +                                                                                                 
      set htyp 144                                                                                                      
      hi/pl 130 +                                                                                                       

1. The option `` K '' in the command HIST/PLOT keep the histogram in memory at the graphics level to allows updating. If no zone is defined, the option `` K '' is not necessary.
2. If an histogram is kept in memory (automatically or via option `` K '') it is possible to add the content of an other histogram with option ``+''.