What are some recommended portable devices to measure HRV using ECG or Photoplethysmography (PPG) that I can use it to compare with new devices?

Hello, I am looking for a good (affordable with scientific evidence) device to measure heart rate variability (HRV) by Electrocardiograph (ECG) or Photoplethysmography (PPG), and I will use it to...

28 October 2020 555 5 View