Had mixed feelings at the beginning as we had an issue on iPhone 8, which was fixed for HRV4Training, but not for Camera HRV (showing poor results). This is most likely reflected in the reported quality though
2/4
another important point is that at this point it should be clear that PPG vs ECG is not what the conversation should be about. PPG works great and can easily outperform ECG (see Firstbeat + chest strap ranking poorly)
Why? Because HRV is all about how you handle artifacts
3/4
From the data shown in the paper, it seems clear that Firstbeat uses a fixed threshold (20%?) and overcorrects for high HRV. This is marketed to athletes and clubs that think it is the gold standard... 4/4
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