A power meter is a device on a bicycle used to measure the power output of the rider. Stages Power meters are all crank-based and use strain gauges to measure the torque, or flex, in the crank arm. The torque data collected as well as cadence are used to calculate power, as displayed in watts, and used to determine the riders’ effort. All Stages Shimano Power meters are Stages Cycling's power meter technology based on a crank arm from Shimano.
For all DURA-ACE and Ultegra left-side crank arms, the model numbers are interchangeable within each model. For example, if you have a DURA-ACE 9100 left crank, you can purchase a DURA-ACE 9200 Stages Power left crank. This applies to left sided cranks only.