marchyman
Cam Killer
You're very lucky and have an unusual hexhead.
Maybe not so unusual. Or perhaps it is a GS thing. I've personally checked 3 hexhead GS. Others GS owners I've talked to report the same. < 2 MPH error when compared to a GPS. Also, last week a friend reported his new, 90th anniversary RT is < 2 MPH fast when compared to his GPS.
For Paul: It's EU council directive 75/443/EEC (pdf) that reads:
4.4. The speed indicated must never be less than the true speed. At the speeds specified for the test in 4.3.5 above and between these speeds, there shall be the following relationship between the speed indicated on the dial of the speedometer (V1) and the true speed (V2):
0 ≤ V1 - V2 ≤ V2/10 + 4 km/h