The shimano xtr m980 and m985 stages power meter replaces either their shimano m980 tripledouble or m985 model double left crank arm add power to existing cranksets by selecting the crank length of your existing crank arm as well as the matching crank model to account for a differences in the arms offsetspecifications accuracy 2 weight only adds 20gr to base crank arm battery life 200 hours coin cell cr2032 power range watts 0 2500 cadence range rpm 20 220 frame com