Has anyone out there ever checked their speedo's accuracy over a measured kilometre (e.g. on the M4, M5, F3 etc.)with a stopwatch? I regularly test both vehicles that I drive and find that with both vehicles (a 1999 Mitsubishi Express Diesel van and a 1995 EF XR6) at 120km/h on the dial actually travelling at 112km/h and 114km/h respectively. There seems to be some algorithmic error because at 110km/h on the dial they measure 104km/h and 106km/h respectively. I had a 1995 Mitsubishi Express Diesel van and its results were identical to 1999 model. Is there some sort of error in all vehicles? Any ideas out there?