Originally Posted by
HardyWeinberg
And I don't think any calibration is ever too precise. I can roll out my front tire over and over and over and never get the same perimeter down to the mm (never mind subsequent pressure changes etc...), although whatever rollouts I do get, they definitely aren't the same as the one listed in the table in the computer's manual...
Even down to 10mm over a few revolutions on a rollout would be an error of < 0.1%, which would be more than acceptable. Compare that to the 6% difference in the two cyclocomputers the OP has.
I calibrate mine from the mile markers on our local rail trail. My cyclocomputer is extremely precise but (naturally) has no inherent built-in accuracy. The milemarkers are set by a GPS device, so they're very accurate over long distances - +/- 30 feet over as many miles as you care to measure. Doing it that way, I can get mine calibrated very well with very good accuracy and precision.