I haven't checked mine out, but I'll compare it w/ my wife's golf and report back in the next few days.
I seem to remember reading somewhere not too long ago that some european speedometers may overstate your actual speed a little. Something to do with the laws in europe being very strict on speedometers that understate the speed, so the manufacturers tend to err on the high side. I'll try to find that article.
In the initial vtec.net review of the Si, they did confirm using a GPS that the speedometer was accurate at 50 and at 80mph.
So my wild guess is that yours is right and the VW's is high.
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