The Cateye ISC-11 Speed Sensor Kit is an ANT+ sensor design to pair with the Stealth 50. Anyone wanting to get the most out of cycling - especially beginners should be aware of cadence. Maintaining a 90-100 cadence encourages an efficient pedal spin that balances the output of the leg muscles and cardiovascular system. Keeping the cadence in the right zone also encourages proper shifting and use of the gears plus can reduce many injuries caused by low cadence gear grinding. The speed portion give you speed while on a trainer plus in areas where satellite acquisition may be spotty.