The Powerbox Carbon double sided power meter chain set from FSA. The Powerbox Carbon crank arms are hollow carbon with a UD carbon finish. The Powerbox is accurate within two percent, delivering accurate data in all environmental conditions. The Power meter features a built-in accelerometer that calculates the riders cadence and battery change indicator. The battery lasts between 300 and 400 hours. An auto zero feature re-zeros the power meter after the rider stops pedalling for more than three seconds. The power box uses ANT+ and can be upgraded to transmit via Bluetooth with the purchase of a firmware upgrade. The software can also be upgraded to feature balance left and right balance.