$header{"Number of Drills"} = &{ sub {  
                                     my $ret;
                                     foreach my $l ( @drill_arr ) {
                                         foreach ( values %{$l->tool} ) {
                                             $ret += $_->count;
                                         }
                                     }
                                     return $ret;
                                 } };

##</code><code>##

my @layer_list   = grep { $_->{layer_type} eq "signal" || 
                          $_->{layer_type} eq "mixed"  || 
                          $_->{layer_type} eq "power_ground" } 
                   grep { $_->{context}    eq "board" } 
                   @matrix_array;