I am using a 19" monitor at 16:10 aspect ratio (1440x900); it is correct even when changing resolution while keeping the aspect ratio the same. I have no idea if aspect ratio matters, but also keep in mind to have the page at 100% zoom (I remembered I kept the browser at 90% zoom as default).

PILE OF SHITE

Perfectly Correct

Perfect!

just trying to figure out how big is 2:30x40cmx2?