The speed sensor 2 attaches to the hub of either wheel and self-calibrates with your edge cycling computer or compatible garmin device to give you accurate speed and distance at all times — even without a head unit. The cadence sensor 2 fastens to any size crank arm and measures pedal strokes per minute so you can get the most out of your training. Send live speed, distance and cadence data to compatible training apps or displays by using ant+ connectivity and bluetooth low energy technology. The odometer feature — for the speed sensor only — tracks your distance to help plan for bicycle maintenance.