Can the Monastery angels enlighten me please on where/what I am doing wrong?

You forgot how to count :)

use strict;
use warnings;
use Tk;
use Tk::ProgressBar;

my $percent_done=0;
my $mw = MainWindow->new(-title => 'Processing');

my $Progress = $mw->ProgressBar(
                 -width => 30,
                -from => 0,
                -to => 100,  ####### <<<< NOTE THE UPPER LIMIT
                -blocks => 50,
                -colors => [0,'blue',100,'blue'],
                -variable => \$percent_done
                   )->pack(-fill => 'x');

for (1 .. 133)####### <<<< NOTE THIS GOES PAST THE UPPER LIMIT
{
    print STDOUT "$_\n";
    $percent_done = $_;
    $mw->update;
    select undef, undef, undef, 0.1;
}
MainLoop();
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