What is Heart rate variability (HRV)?
Variation in time between heartbeats; SDNN is a common summary metric in consumer apps.
812 · 768 · 845 ms · it varies
Which statement fits Heart rate variability (HRV)?
Answer it in your own words in the app.
In real work
Lower HRV after poor sleep is common; trends matter more than one reading.
In the illustration
Paper runs at the standard 25 mm/s. Calipers span the last two beats: 812 ms, then 768, then 845. That beat-to-beat change is HRV.
Chart my Heart rate variability (HRV) in your health app by week since January, explain what SDNN is, and what changes it from day to day.
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