The subatomic spider houses integrated electronics, a CR2032 battery, LED indicator & visible ANT+™ ID. Omni Cal™ gives you a choice of chainrings with no compromise on accuracy. The Exogram™ Hollow Carbon crank arms by SRAM reduce weight & increase performance. The only visible power component is the low profile, all aluminum battery case & the new stress flow lifts accuracy to +/- 1.5% & makes power measurement independent from chainring selection. Omnical™ Power measurement is independent from chainring selection. Swap chainrings without impacting accuracy. No recalibration necessary Exogram The new Hollow Carbon Construction starts in the crank arm & extends into the cranks’ spider. It maximizes the stiffness to weight ratio.