use strict;
use warnings;
use Tk;

my $mw = MainWindow->new();

my $name = $mw->screen;
my $height = $mw->screenheight; 
my $width = $mw->screenwidth; 
my $scaling = $mw->scaling;
my $heightmm = $mw->screenmmheight; 
my $widthmm = $mw->screenmmwidth;

print <<EOT;

screen name     $name
pixel width     $width 
pixel height    $height 
scaling         $scaling 
mm width        $widthmm
mm height       $heightmm

EOT

MainLoop;

##</code><code>##

screen name     :0.0
pixel width     1920
pixel height    1080
scaling         1.33333333333333
mm width        508             # <--- wrong!
mm height       286             # <--- wrong!

##</code><code>##

Get-WmiObject  -Namespace root\WMI -ComputerName localhost -Query "select InstanceName, MaxHorizontalImagesize, MaxVerticalImageSize from WmiMoninitorBasicDisplayParams"

...

MaxHorizontalImageSize : 48
MaxVerticalImageSize   : 27