Optical HR monitors aren't that accurate. They are only useful if your analysing trends over time. People that buy these fitness trackers and expect medical level accuracy are either misled by deceiving marketing or not doing enough research.
* they were all within 5bpm
Hopefully there'll be some sanity with how this is handled...
I've checked the reading three times by comparing with my radial pulse, counting against my wristwatch. Each time it was bang on, or within 2bpm.
That's when fairly inactive, though. Will have to check it's consistent at much higher pulse rates.