Originally Posted by
prathmann
In the OP, the reported distance is about 23% lower than that of his friend. That's a big discrepancy and the suggested changes in the circumference between 2096mm, 2114mm, or 2084mm are very small in comparison (less than a 2% variation). So there must be another reason. Either this cyclometer uses something other than the usual circumference in mm as the distance setting, it's defective, or possibly the magnet is placed a bit too far from the sensor and some of the distance was not recorded.
23% is too big to be a calibration issue, it's probably the magnet too far from the sensor. You'll probably need to make sure the magnet is proud of the spokes, and then rotate the sensor around on the fork to get it as close as possible to the magnet without touching. Also make sure the magnet is correctly located on the spoke, so the center of the magnet passes at (or very close) to the centerline of the sensor. (The sensor centerline is usually marked with a line on the plastic housing.)