@JasonW-1990 I am not a mechanical engineer, but I read a lot about how thus stuff works. The heart rate LED emitter gives off the green light which is reflected back to the sensors. Most of your tendons that move your fingers are covered by the emitter/sensor when you wear it on the underside. This gives a kind of interference called optical noise when you move your fingers. Everything I read says that the heart rate is less reliable when you wear it facing the inner wrist.
Laurie | Maryland
Sense 2, Luxe, Aria 2 | iOS | Mac OS
Take a look at the Fitbit help site for further assistance and information.
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