PMeter

PMeter is a very useful tool which displays a virtual ruler on your desktop, thus allowing you to make various measurements. It can be easily installed and configured.
The interface of the application is based on a long frame which resembles a yellow ruler. By default, it stays on top of other windows and can be moved to any position on the screen, with the help of the mouse cursor.
By opening the context menu, you can go to the Settings screen, in order to set up the three configuration modes. Therefore, you can write a name, width, label (no label, ruler or screen coordinate) and scale (e.g. unit, granularity).
In addition, you can alter the default background and cursor line colors, enable transparency mode, use a magnifier and customize it (zoom level, crosshairs, horizontal, vertical), configure handling properties (e.g. double click, snap to axis, button), as well as set parameters concerning the pixels per inch and preset lengths. Plus, you can make PMeter automatically run at system startup and to display a color picker.
The tiny tool requires a very low amount of CPU and system memory, and is pretty responsive to commands. We have not come across any difficulties in our tests; PMeter did not hang, crash or pop up error notifications. Thanks to its intuitive layout and overall simplicity, users of any level of experience can figure out how to work with this program.