This works exactly as it should- I have one on my cross-country mountain bike and it took about 10min to install. Love that it starts up and stops with your activity (based on rotations of the wheel) and makes me push myself a little bit further than I normally would by seeing stats. UPDATE: I've also bought a 2nd unit and installed on my winter training spin bike- although there's no way to properly calibrate actual speed/distance on a spin bike, the relative speed/distance are something I monitor in a workout and the timer is also helpful. I would recommend this to a friend ;-)