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Can I Use a Cadence Sensor When Using Garmin Power Meter Pedals
Rally and Vector pedals use integrated accelerometers to measure cadence when cycling. This feature eliminates the need for any separate cadence sensor or magnet to be installed.
If you are already using a cadence sensor such as the Garmin Bike Cadence Sensor 2, the cadence readings from the Garmin pedals will override any other data. Leaving these other sensors installed will not cause problems, but their data will not be recorded or displayed.