Use your monitor as a ruler

If you ever find yourself in a quick pinch for a ruler to measure something, use your monitor.  Try iruler.net.  When you go there, it will determine your monitor size and resolution and display a nice ruler in the middle of the screen that is exact according to your monitor dimensions.  Yes, it works, I had to verify that a 2.5 sata hard drive was indeed 7 millimeters instead of the standard 9.5 millimeters and it verified it for me.