Old-car speedo back-up.
For many years I have used the Union in vintage cars. Strapped to the steering wheel or mounted on the dash board, the Union is absolutely accurate - which is more than can be said of most 90-year-old speedometers - and can give useful information such as average speeds and highest speed attained (good for boasting).. I have sometimes found the Union ceases to work in very wet conditions.
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