Harry Bloomfield wrote:
Dave Plowman (News) brought next idea :
Quite. Although even eddy current speedos could be far more accurate than
that spec.

Then there were chronometric ones. You'd laugh at a clock which couldn't
better 10% accuracy even in the 19th century.

Yep, the calibrated speedo in traffic cars.

My ex police bike speedo (cable driven) reads the same as GPS, all other
vehicles have read over.