Rob ter Horst uses his Polar H10 chest strap as a reference device and says it is his gold standard ECG device for research. According to this information is possible to build a highly accurate ECG device for a very prize: The Apple watch Ultra currently costs about 800 USD at digitec Switzerland: https://www.digitec.ch/de/s1/product/apple-watch-ultra-ocean-49-mm-titan-4g-sportuhr-smartwatch-21996973 A …