I like this, but the calibration method is a little difficult. My preferred method is to enter a good guess of the monitor size, and then compare a virtual rule with a real rule until they are equal. A nice example is <a href="http://pective.com/pic/10-cm-ruler" rel="nofollow">http://pective.com/pic/10-cm-ruler</a> because it has international and imperial units.<p>Also, entering the monitor size is difficult because it opens a new mini-window without the old value. I’d like to have the old value and be able to edit it as text or use a up/down button to make small changes.<p>I used a similar method to copy the format of a document from Word to LaTeX. In my monitor, with a 141% zoom the image has the actual size, so I can compare the margins and line separations and size of the logos.