The stages power meter g2 si hg crank is the power meter option for all cannondale bb30 riders who are on a cannondale si hg crankset the g2 si is pre assembled on a si hg left crankarm and will also retrofit to sisl2 cranks it replaces the existing left crankarm which makes installation pretty simple due to the left crankarm interface there is no interference with the drivetrain components this power meter uses a custom strain gage array to measure power at the left arm by measuring power