The RS400sd is designed for the analytical runner who demands more information.The ability to plan, monitor and analyze training data including speed and distance at your fingertips.Polar exercise featuresWireless ECG accurate heart rate.Polar sport zones.Polar OwnZone®.Polar OwnCal®.Polar Fitness Test™ with OwnIndex®.Polar OwnCode® (5kHz).Polar OwnOptimizer™.HR-based target zones with visual alarm = 3. HR-based target zones with audible