Been there, seen that, all I got was this lousy t-shirt.

From the system I maintain:

  /*
 e - ExternalStatus
 i - InternalStatus

          e\i  |   D    F     N   X
          --------------------------
          D    |   A    B     C   D
          F    |   E    F     G   H 
          N    |   I    J     K   L
          X    |   M    N     O   P 

*/

  switch( $inst->Status ) {
   case 'A' : 	case 'D' : case 'M' :
    $stats['d']++; break;
   case 'E' : case 'F' : case 'G' : case 'H' :
   case 'B' : case 'J' : case 'N' :
    $stats['f']++; $stats['d']++; break;
   default : $stats['n']++;
  }