Speedo Readout
 

I've discovered that my analogue speedo is about 4 km/hr out. For example if I set my cruise control on when the speedo reads 100 km/hr, my satnav (not the inbuilt one but an external Garmin unit suction cupped to the windscreen) reads a stable 96 km/hr. This reading from the satnav is corroborated by doing an average speed reset on the MID while cruising. It reads 96 km/hr also.

Is this common ? That the speedo reading is overstated ?

It is over-reading by design.

German law requires speedo accuracy to be within a certain range, essentially up to a few percent over, but not under at all. Because of production tolerances, and the penalties for under-reading, all of them are designed to read high. It is usually more than 4 km per hour at 100.

It is only the speedometer, the odometer is accurate.