The Mi band 2 is a successor to the mi band 1s all the key features are same but with some minor changes but which has totally changed its value . The major improvements include and OLED display, heart rate sensor , and improved battery life.The battery lasts for 30 days once charged completely. The accuracy and perfection is phenomenal with the mi band 2. It measures your heart rate , calories burned, steps taken and shows it on to the screen. The band is a great quality band with irritation free material , specially for those have skin related alergies. It is fully waterproof so do not mind wearing it for swimming or while taking a shower.Comes with bluetooh , accelerometer and oled for the display. If you are a fitness geek then this one is the one you must buy for sure.