In one example, a structure for attaching a wheel to one of a frame of a motorcycle or a bicycle may include an axle having first and second opposing end portions and supporting a wheel, a left axle support collar structure configured to support the first opposing end portion of the axle, and a right axle support collar structure configured to support the second opposing end portion of the axle. Differences in the fluctuations of the supply voltages that are supplied to the sensor unit and the signal detecting unit essentially result in the generation of undesirable fluctuations in the measurement signal. By outputting the information on the accessing of the internal bus by the internal CPU to the debugging unit, the system monitoring unit can output the state of the internal bus while controlling the internal CPU to operate. In an alternative preferred embodiment, the midsection spacer is a solid unit, joining two halves of a small diameter shaft.