I recently had a “computer” attached to the bike and that changed the way I ride. Jose who attached it did an excellent job, but I wondered about the calibration.
I found a spot in the ride that was exactly 5 miles in and compared that to the odometer. It looks like they agree within 1-2% which in this case is 250-500 feet.
In thinking about this I realized that Google Maps, which I used as a source for my data only represented 2 significant digits (5.0 miles) and my odometer had three (5.00).
I do want to test further but I am already at the limits of Google.