But how do fitness trackers measure your heart rate, exactly? And how accurate are these measurements? We asked the experts.

This measurement, known as heart rate variability (HRV), has emerged from relative obscurity to become one of the most revealing biomarkers in modern health monitoring. Far from indicating ...

As Hall explains: According to Apple, putting your finger on the Digital Crown to capture a heart rate reading also measures faster and with more accuracy as it updates every second versus every five ...