Hello, we just bought the above c-computer and set the calibration according to the manual chart for the wheel size of 700x23. However, the speed, and average speed is off by 0.4 mph over a 30 mile ride, for example (reads low). My computer is accurate based on past use with cue sheets. In the past when my husband and I rode together, using identical c-computer, the difference in readings was not this significant. This computer uses circumference in millimeters to set - see(http://sheldonbrown.com/cyclecompute...n.html#formula). Sheldon Brown's site suggests that I should set the calibration at a number (2097) higher than that recommended by the manual (2096). This seems like it will help (thinking about geometry and circumferences). Any thoughts? Also, are the wireless less accurate than the wired?