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.Key Features: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 powerBluetooth and ANT+ with wireless firmware update and data acquisition systemEasily rechargeable integrated battery with fully waterproof reliable electric systemHollow outer chainring, giving vast improvements in rigidity and increased weight savingsThe hollow outer chainring has essentially removed outer chainring flex, hugely improving shift performance making it precise even under high loadThese industry leading HollowTech II cold forged hollow crank arms have evolved to increase rigidity, reduce weight, and improve strengthThe teeth have be