A  B   C  D  E   ...  M   N  O   P
1 x1  .  x2  . x3   ... x7   .  x8  .    
2 ---------------------------------------- # row of separation
3 x9  .  x10 . x11  ... x15  .  x16 .
4 ----------------------------------------
5 x17 .  x18 .           ...etc
6 ----------------------------------------
...
24