I did a test today, I compared my Micra's speedometer with that of my GPS. I was surprised to find it off by 5 KPH.
http://mymicra.com/P6100058.JPG
It seems to be less off at lower speeds, and more off at higher speeds.
After that, I decided to reset my trip counter in both the Micra and my GPS at the same time. After the Micra showed 80.4km of travel, the GPS showed 78.06km of travel.
Has anyone else noticed this?