Thanks to 
4iiii Innovations it has never been easier to get started training with power. With industry-leading accuracy, incredible ease of installation, the Left Side 
Ride Ready Powermeter will help you train smarter and more efficient. Available in 105, Ultegra, and Dura-Ace left crank arms, the
 Ride Ready ships installed. Simply replacement your stock left crank arm with the
 Ride Ready using the existing cranks Hollowtech II interface. The
 4iiii Powermeter is compatible with ANT and Bluetooth head units. Ride and train smarter with 4iiii. 
- Data Accuracy within /- 1.5% error margin
 - 100 riding hours of battery life on replaceable CR2032
 - ANT and bluetooth compatible
 - Power unit adds just 9 grams to crank arm weight
 
In order to ensure chain stay clearance, print the 
compatibility guide prior to ordering.