If you want to recalibrate your speedometer, I would suggest doing this.
Take the gauge window off.
Pull the needle off.
Put it into test mode (hold down the trip button and keep holding it when you start your car. Then it'll flash and your needles will jump. Hit the trip again I think 4 or 5 times until you get to 000.0. That's a digital read out of your speed).
Cruise on an open road to about 30 - 40 miles an hour
Then carefully push the needle back on right at what your digital read out says.
Helps to have a friend with you. I'm not sure if that'll negate putting on unwanted miles though. And many people will say that this method is not the best way to do it. I did this and now my speedometer is now more accurate than it used to be factory. I think they make it look like you're going faster than what you really are by default.
Hope that helps, or someone can chime in with more knowledge about the needle calibration.
And crap tonz more of info can be found here:
http://www.focusfanatics.com/forum/showthread.php?t=65218&highlight=complete+archive