^            t                                                                
  |            t  t                                                             
  |   t     t  t  t                                                  t          
  |   t  t  t  t  t  t  t                                            t  t       
  |   t  t  t  t  t  t  t  t                                      t  t  t       
  |   t  t  t  t  t  t  t  t  t                                t  t  t  t       
  |   t  t  t  t  t  t  t  t  t  t  t                          t  t  t  t  t    
  |   t  t  t  t  t  t  t  t  t  t  t                       t  t  t  t  t  t    
  |   t  t rt  t  t  t  t  t  t  t  t rt                 t  t  t  t  t  t  t    
  |   t rt rt  t  t rt  t rt  t  t  t rt  t rt  t  t  t rt  t rt  t  t  t rt    
 -+---------------------------------------------------------------------------> 
  |  13 14 15 16 17 18 19 20 21 22 23 00 01 02 03 04 05 06 07 08 09 10 11 12