my $LB = 'LB';
my $LENGTH_RANGES = 'LENGTH_RANGES';
my $WIDTH_RANGES = 'WIDTH_RANGES';
my $EM_POLY = 'EM_POLY';

# ...sometime later...
$metals{$LB}{$LENGTH_RANGES} = [ 0, 10 ];
$metals{$LB}{$WIDTH_RANGES} = [ 0, 1.080 ];
$metals{$LB}{$EM_POLY} = "(-0.665364 + (9.6216 * W))*(10/L)";