use Tk;
use Tk::Font;

my $mw = MainWindow->new;
my $font = $mw->Font(-size => 12);

foreach (1 .. 10) { 
   $mw->Label(
      -text => "Test",
      -font => $font
   )->pack;
}

$mw->Button(
   -text => "Enlarge Font",
   -command => sub {
      my $size = $font->configure('-size');
      $font->configure(-size => ($size + 1));
   }
)->pack;

MainLoop;