Environmental factors such as high temperature and altitude impact your training and performance. For example, high altitude training can have a positive impact on your fitness, but you may notice a temporary VO2 max. decline while exposed to high altitudes. Your D2™ Mach 1 watch provides acclimation notifications and corrections to your VO2 max. estimate and training status when the temperature is above 22ºC (72ºF) and when the altitude is above 800 m (2625 ft.). You can keep track of your heat and altitude acclimation in the training status glance.