my $input = $mw->Entry(-takefocus => 1,
    -textvariable => \$upper_no,
    -width => 12)
    ->place(-relx => 0.50, -rely => 0.05);

my $counter_label = $mw->Label(-textvariable => \$no,
     -relief => 'sunken',
    -anchor => 'center')
    ->place(-relx =>0.0, -rely => 0.80, -relwidth => 1.0, -relheight => 0.2);

# When <enter> is pressed, this taken into the action.
$input->bind('<KeyPress-Return>', sub {
                count();
                $counter_label->configure(-textvariable => \$no);
            }
        );