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.