To allow the accelerometer to calibrate, always install the Gravity+ on your bike before powering it on. Hold the power button down for 1 second to turn the light on or off. Then, keep your bike still for 1 second after pressing the power button to complete the calibration. 

Specifications

• Automatic accelerometer brake light function shines 100 lumens bright
• 2 Modes (runtime): Solid - 20 lumens (12 hours), Flash - 80 lumens (30 hours)
• USB rechargeable li-polymer battery
• Weatherproof exterior for all season riding
• Seatpost and backpack clip mounts included
• Mounts vertically or horizontally
• Includes USB-C recharging cord
• Weight: 1.9 oz