How does this code calculate the "left" attribute?

[Nasr]

var ctrlOffset = $(e.target).coords(),
                overlayOffset = this.overlay.getOverlay().coords();

            this.overlay.getOverlay().css(
            {
                left: ctrlOffset.left + ctrlOffset.width - overlayOffset.width,
                top: ctrlOffset.top + ctrlOffset.height + 5
            });

I found this code in inline_mod.js. I think this deals with the inline mod overlay being positioned when the checkbox is clicked. I'm getting a "left: 1070.5px" result where as I just wante to get a 500px instead. I'm not sure how this calculates things. Looking for some help if possible.

I need to edit this because I have changed my forums to RTL right now until full RTL support is officially provided.