The Dura Ace R9100 Power Chainset from Shimano. After years of development and working with pro teams the Dura Ace R9100 Power Chainset is the result. The R9100 Power Chainset uses highly accurate strain gauges in both left and right crank arm providing accuracy within 2 percent. The R9100 Power Chainset is compatible with Bluetooth and ANT+ devices for wireless firmware updates plus data acquisition. The chainset uses an internal battery with a waterproof cover. The hollow outer chainring and Hollowtech II crank arms increase stiffness whilst keeping weight low.