use Tk;
use lib ".";
use Tk::waitVariableX;
my $break;
sub start_it{
    $break=0; while (!$break) {
        my $result = foo($a1, $a2);
        $detail->insert("1.0", $result);
        $mw->waitVariableX(3000, \$break); # cf EMU-book
    }
}
sub stop_it {
    $break = 1;   # set by mou-click
}