When launched, Screen Ruler will appear horizontal showing approximately 400 Pixels in length. When ever your cursor is over Screen Ruler it will change to cross-hairs and the distance of the cursor from the left (0) of the ruler will be displayed next to the Size Slide Control.
The "X" Button: This will close Screen Ruler.
The "--" Button: This will minimize Screen Ruler. To reactivate the program - just click on the minimized box.
The Size Slide Control: You can adjust the size of Screen Ruler by using the Slider control.
Moving Screen Ruler: To move Screen Ruler to the desired location - simply place your cursor anywhere on the Ruler, left click and drag while holding down the mouse button while dragging.