Gnuplot bar chart with Perl: how to put values ​​on top of bars

How can the following gnuplot be generated using Perl? (I need a histogram where, under each bar, I will write the difference between this column and the column on the right side with the same data)

The problem is I didn't figure out how to put numbers under the columns using Perl.

This is the gnuplot code:

reset

set terminal png 

set output 'StackOverflow.png'

set style fill solid 1.00

set style histogram clustered gap 1

set style data histograms

set yrange [0:120]

set xtics norangelimit font ",8"

set ytics norangelimit font ",8"

set key font ",8"
set key width -8

xoffset=0.17
yoffset=0.03

plot 'data.dat' using 2:xtic(1) with histogram title "Parameter 1", \
     '' u 3 with histogram title "Parameter 2", \
     '' u 0:2:4 with labels offset -0.9,0.5 title "", \
     '' u 0:3:5 with labels offset 2.0,0.5 title ""

      

        
        
        
      

    

I have currently created the following using Perl:

And this is the Perl code:

#!/usr/bin/perl -w
use strict;
use Chart::Gnuplot;

my $chart = Chart::Gnuplot->new(
    output => 'plotStyle_19.png',
    yrange => [0, 120],
    bg     => {
        color   => "#c9c9ff",
        density => 0.2,
    },
);

my @x = qw( A B C D );
my $h1 = Chart::Gnuplot::DataSet->new(
    xdata => \@x,
    ydata => [99, 97, 97, 95],
    title => "1st data set",
    color => "purple",
    fill  => {density => 0.2},
    style => "histograms",
);

my $h2 = Chart::Gnuplot::DataSet->new(
    xdata => \@x,
    ydata => [9, 10, 13, 15],
    title => "2nd data set",
    color => "dark-green",
    fill  => {density => 0.2},
    style => "histograms",

);

$chart->plot2d($h1, $h2);