I think with all these devices "accurately" is a loose term in the sense that it is accurate enough, but could be better. Wrist based ECG has been determined as

I think with all these devices "accurately" is a loose term in the sense that it is accurate enough, but could be better. Wrist based ECG has been determined as accurate enough to wear on your wrist, but isn't as accurate as what you'd get in a hospital. If it is accurate enough, then the particular number isn't necessarily the important, its whether it an measure the same number consistently, then track movements from the baseline. Which is why they often have a % up/down accuracy figure.