Calibration
Once a new computer is installed, it usually requires proper configuration. This normally includes selecting distance units (kilometers vs. miles) and the circumference of the wheel. Since the sensor measures wheel rotation, different wheel sizes will translate to different measures of speed and distance for a given number of rotations.
For more accuracy the bicycle (with the set cyclocomputer) must be ridden by the intended rider over an accurately measured distance. The computer's reading is then compared with the known distance and any necessary corrections made.
Read more about this topic: Cyclocomputer