How Did Photoplasmography Measure Heart Rate Variability Continuously?

The first device to measure heart rate was a $20,000 piece of medical technology in a hospital. The company used photoplasmography using light to shine underneath your skin and be able to accurately measure heart rate variability. "We were much more focused on how can we measure something about the human body that's ultimately medical grade, but presented to you in a consumer form factor," says co-founder John Defterios.