E90 speedometer error - can calibrate?

You can't have owned much of a selection. Rover of all people used to fit accurate speedometers as did Jaguar and Rolls. Others too, possibly. I have an SD1 Rover dating from the mid '80s and that is exactly accurate at 30 mph - or at least as accurate as you can read with an analogue instrument. At 70, it reads 71. Checked on a rolling road with new tyres. Contemporary road tests also bear this out.

Absolutely. A cheap DVM that measures frequency will be accurate to within 1% As should a speedometer with the correct new tyres. Worn out tyres introduce an over-read of approx 2%.
If it were manufacturing tolerance, some would be accurate, some over read a little and some up to the maximum. But the error is pretty consistent so must be deliberate.
*A plateau is a high form of flattery*

Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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