Rugged by design The resilient athletic design features a 1.2' solar charged display, responsive touchscreen, traditional buttons and 42 mm fiber-reinforced polymer case with a steel bezel and rear cover. The watch is tested to U.S. military standards for thermal, shock and water resistance. Long battery life wih solar charging Get up to 14 days in smartwatch mode with solar charging in 3 hours of direct sunlight (50,000 lux) per day and up to 46 hours in GPS mode with solar charging (assumes continuous use for entire period in 50,000 lux conditions). Built-in LED flashlight Variable light intensities and a red safety light give you greater awareness while you train in the dark and can provide convenient illumination when you need it. Strobe mode can even match your running cadence. Hill score This feature measures your capability for running uphill and evaluates your progress over time based on your VO2 max and training history. It measures your running strength on steep ascents and running endurance on long ascents and provides a score based on your performance over time. Endurance score This feature measures your ability to sustain prolonged efforts and combines training data from all your athletic pursuits to help you understand how training impacts your overall endurance. Knowledge is power Your health and training data should be easy to interpret and provide actionable insight. Begin each day with a customizable morning report, and see a daily summary of health and wellness information.