Always up for a swim, with water resistance up to 50 meters. Custom swimming mode tracks swim times, calories burned, and more. Optical heart rate monitoring technology lets you check your stats anytime with a flick of your wrist. Get a more holistic picture of your health with 24-hour heart rate tracking. Heart rate zones – warm-up, fat burning, aerobic, anaerobic,and extreme – help you precisely track and optimize your workouts. Measure your heart rate with greater accuracy thanks to M4 core technology, support for floating-point operations, and an optimized algorithm.