Despite having tried almost everything (scanned through all settings, HR always on, using Samsung Health and Strava, have been wearing very tight to very loose, have been wearing higher up or lower down on the wrist, ...), and reading all the posts, blogs and reviews I could find, I still cannot get any reliable measurement out of this watch. You can find some of the traced attached. The 2 primary concerns are:
1) Given all the flat lines over gigantic periods of time and distance, probably this watch hardly ever detects a heart rate accurately.
2) Given the extremely smooth line as compared to any other watch ever sold on the marketplace, my confidence on extracted heart rate is extremely low, in these parts where it actually doesn't report a flat line.
I am willing to accept that accuracy may be a bit less during running, yes, I know it's challenging for all watches, but this is an absolute random number generator. For a watch which claims to go head to head with Apple Watch, this unbelievable.
I am completely baffled that nobody reports this as a serious issue.