Pioneer's Shimano Dura Ace 9000 Power Meter is a revolutionary power meter that attaches stealthily to the left crankarm. The Dura Ace 9000 left crank arm meter allows every rider power-based (also called watt-based) training performance, allowing you to fine-tune your pedaling to find race-winning form without breaking the bank. With advanced technology accurate to +/- 2%, ANT+ transmitting, active temperature compensation, and a mere 22 grams of weight, the Pioneer power meter is perfect for any cyclist. Additionally, installation is fast, simple, and clean with zero wires, magnets, or zip ties. If you find yourself addicted to the data and crave more, upgrade kits that retroactively add drive-side power are available (sold separately).