Anyone know how to calibrate the navigation system?

[Green Machine]

While driving back on 101 S from a weekend trip to San Jose, I noticed that the nav showed me as being a few hundred yards to the east of the 101. Now that I'm home, the navigation system seems to be way off. It shows me as being in another nearby city. Is there a way to reset the nav?

I came across this but it didn't seem to work.

http://www.ehow.com/how_7585158_instructions-using-gm-oem-navigation.html