Hi Brian, the "Center on page" option will appear if you set Scale: "Preserve units" instead of Scale: "Fit to page".

@David - I think I broke that with some recent fiddling with PDF output as part of the work for exporting dimensions to PDF. Can you please send me an e-mail (moi@moi3d.com) and I'll send you a test build for a fix?

Thanks, - Michael