IIRC, there needs to be a sensor on the front fork, which sends a signal when a magnet passes under it. One common problem is that the magnet and sensor get too far apart. Rather than fool around trying to get the gap correct, and then losing it on the first ride, get some small neodymium magnets from a hardware store and attach one or more to the 'puter's magnet. Then the gap becomes easy to set and keep.