With several years of development and working closely with professional teams you can expect extreme accuracy from Shimano's first fully integrated power meter HollowTech II 12-speed Dura-Ace chainset. Accurately calibrated strain gauges are integrated inside both left and right crank arms this provides a stable measurement system through rotation from both sides for extremely precise data. +/-2% accuracy of strain gauge measured power Bluetooth and ANT+ with wireless firmware update and data acquisition system Easily rechargeable integrated battery with fully waterproof reliable electric system Hollow outer chainring giving vast improvements in rigidity and increased weight savings The hollow outer chainring has essentially removed outer chainring flex hugely improving shift performance making it precise even under high load These industry leading HollowTech II cold forged hollow crank arms have evolved to increase rigidity reduce weight and improve strength The teeth have been developed to work only in conjunction with the 12-speed chains for improved contact providing more efficiency and improved power transfer There is a wide range of chainring ratios and crank arm lengths available enabling customisation for all riders and racing disciplines HollowTech II integrated bottom bracket design uses a wider bearing placement and larger axle diameter for increased stiffness and efficiency Bottom bracket seal design has a minimal bearing interface gives superbly smooth rolling and increased durability