For anyone who has not tried to check a speedo on the "measured mile" at 30 mph one mile takes 2 minutes. There are two issues to check. One is that the speed indication is correct and the other is that the distance measured is correct. Best to do it in two runs, one for distance (so that you can start and stop at the posts to check the odometer) and the other to time the run at a constant speed. Best done with a passenger armed with a stopwatch.

It is not easy to keep a constant speed over a mile.

Peter

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