Quarq's Elsa RS Power Meter Crank Arms bring watts measuring functionality to your Shimano drivetrain so you can bring a touch of intelligent design to your training plan and racing strategy. The unit's Power Balance feature generates power numbers for both arms, so you can better identify weaknesses in you pedal stroke. It also features Quarq's 10k dynamic compensation technology, which uses a map of 10,000 data points ranging from zero to 130 degrees Fahrenheit to automatically adjust its readings when temperature variations get extreme. This minimizes drift and helps avoid the necessity of multiple mid event zeroings, so you won't be stuck freewheeling to reset your readings at a crucial moment when the race is hotting up in miserable conditions. Unlike with similar models from other manufacturers, Quarq's batteries can be changed with a simple tool at home instead of being mailed in to the factory for servicing. The unit is finished with an AxCad accelerometer so your cadence isn't lost in the watts parade, and since it measures those watts with an industry leading 1. 5% accuracy you can rest assured that your numbers won't be over or undercooked.