Ive had the 42mm Galaxy watch for about a week. Heart rate sensor is way off during workouts when it's not just flatlining. After doing heavy lifting my heart rate peaks around 180+ bpm yet when I get a reading (if I do get one), it's never over 140... As others have pointed, it seems to get worse when sweating a lot. Tightening the watch does help a bit but it is clearly too uncomfortable to be an actual workaround. Disclaimer: I made sure my firmware and apps were updated, I didn't try a reset yet though.
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