Normally it should work with whatever window is frontmost, but I can’t guarantee it will work properly in every application, because it depends on their support for AppleScript. I unfortunately don’t have a copy of Microsoft Word to test with, but if anyone has a solution, please let me know and I’ll update the post.

If you have, for example, two Word documents open, the script will only apply itself to the document that was initially opened. You can’t toggle between windows and apply the script to the second document.

Is there anyway to jig this script so that it will work with multiple windows of the same application after having switched to the second or subsequent document/window?

Gotta love AppleScript syntax

Thank you for bothering to help. My life is in order again!

That’s because windows with an odd-numbered pixel-width can’t be perfectly centered on a screen with an even number of pixels. Fractional pixel values get rounded automatically.

If you want more control over the rounding, you can change this part:

    set bounds of window 1 to {¬
        (screenWidth - windowWidth) / 2.0, ¬
        windowYt, ¬
        (screenWidth + windowWidth) / 2.0, ¬
        windowYb}

to something like this:

    set bounds of window 1 to {¬
        round ((screenWidth - windowWidth) / 2) rounding as taught in school, ¬
        windowYt, ¬
        round ((screenWidth + windowWidth) / 2) rounding as taught in school, ¬
        windowYb}

It’s kind of wordy, but it tells AppleScript to always round .5 up. Normally, it rounds .5 towards the nearest even number.

You can see full documentation for the different rounding options in the AppleScript 2.1 Help: round document on Apple’s site.

However, the script can actually change the horizontal window size by one pixel.

This is noticeable with Pages if you size the window so that it’s exactly the width of the page (horizontal scroll bar disappears but no background gray appears yet). The script can sometimes make the window 1 pixel wider or narrower depending on the width of the window. Perhaps something to do with odd/even numbers?

Yes, one pixel. But we’re already in freaky obsession territory here! (In pages the one pixel is very noticeable since it makes an ugly dark line appear into the margin, instead of smooth white.)