Polar RCX5 SD RUN Get run-specific training guidance in a unique, easy to use package. The Polar RCX5 SD Run is ideal for tracking your workout data, stride info, heart rate and other workout specific details. Switch from one sport to the next easily, an ideal feature for triathletes. Monitors heart rate even in water and race pace helps control your speed to reach your target time. Download training programs from polarpersonaltrainer.com. Designed for active event runners whose typical events are 10K, half marathon and marathon. ZoneOptimizer: Ensures you're always training at the right intensity. Wearlink Hybrid Transmitter: Transmits in water. Data link: Transmits training data wirelessly to Polar's free training website, polarpersonaltrainer.com. Pace Lock and Race Pace: Helps keep steady pace and set target pace/speed for certain distance. Measures running speed/pace and distance. Helps improve running technique by providing your running cadence and stride length. Determines your Running Index, which tells you about your running performance. Shock and water resistant, handles even the most demanding runs.