The ruler, just like those normally used in schools, is semi-transparent, so you can easily see what's behind it. To move it you just have to right-click on it and drag it where you want.
Some of the features in the program let you increase or decrease the size of the ruler (you can do it with keyboard shortcuts), move it with the arrow keys to be more accurate, or use a virtual magnifying glass to be even more accurate.
You can open and close the program at any time. It barely uses any resources so it's really fast and takes just a second to open up.
Screen Ruler 2D is a pretty useful tool for graphic designers or anyone who has to measure elements on the screen from time to time. No more putting the plastic ruler on top of your screen.
Includes ads announcing it's a trial version.