As a web developer, screen designer or digital artist you often have to measure elements on your screen / browser windows. Aligning is difficult because your website usually doesn't have visual aids or grid lines.
Switching between your favourite imaging software (f.ex. Adobe Photoshop) and your browser (f.ex. Firefox) is time consuming and there is no real help for measuring elements on the screen.
Firebug (a Firefox Addon) is an excellent tool to dermine the height / width of an element. But Firebug works only with elements that have already a fixed size. But the overall width isn't directly visible and it works only for html elements. What is the next step?
Using ScreenRuler, you can measure any distance on your screen. An extra large mouse pointer will help you to point out the exact size of boxes, images and tables on your desktop.