I hope this snippet will help you.

#-- Just for clarity, here is the hash array used in the snippet
my %_MAINWIN = 
  (
    'title'         =>  'Oracle User Manager for Baan ('.$_VERSION.')'
+,
    'width'         =>  790,
    'height'        =>  565,
    'row_height'    =>  25,
    'radioratio'    =>  1.0,
    'buttonratio'   =>  1.0,
  );

#-- Create and center the main window
$mMainWindow = MainWindow->new;
$mMainWindow->title($_MAINWIN{title});
$mWinX = int(($mMainWindow->screenwidth-$_MAINWIN{width})/2);
$mWinY = int(($mMainWindow->screenheight-$_MAINWIN{height})/2);
$mMainWindow->geometry
  (
    $_MAINWIN{width} . 'x' . $_MAINWIN{height} . 
    '+' . $mWinX . '+' . $mWinY 
  );
$mMainWindow->resizable($_FALSE, $_FALSE);
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Anyway, the quick answer is centering is done with geometry. Please post here if you have additional questions (or if I missed the actual question. *Smiles*)

Update Yeah, what MZSanford said... *Smiles*