Stages Cycling's Stages Power Meter is a revolutionary power meter that attaches stealthily to the left crankarm. It allows every rider, in every discipline, power-based (also called watt-based) training performance. With advanced technology accurate to +/- 2%, ANT+ and Bluetooth Smart transmitting, active temperature compensation, and mere 20 grams of weight, the Stages Power meter is perfect for any cyclist whether looking for their first power meter or a savvy power-training expert. Additionally, installation is fast, simple, and clean with zero wires, magnets, or zip ties. This Stages Power Meter model is available as a Shimano Ultegra 6800 replacement left (non-drive) crankarm (shown) or integrated into the crankarm on a complete Shimano Ultegra Standard (53/39-tooth chainrings), Compact (50/34) crankset, or Mid-Compact (52/36) crankset (bottom bracket sold separately).