measure objects on screen with a variety of metrics

 ScreenRuler will display a ruler on screen which allows you to measure the
 other objects that you've there. It has the following features:
  * Horizontal and vertical measurement in 6 different metrics:
    pixels, centimetres, inches, picas, points, and as a percentage
    of the ruler's length.
  * Cusomizable colors and fonts.
  * Keyboard control for precise positioning.
  * Option for the ruler to stay always on top of other windows.