Stability (overnight data) measures two metrics: overnight resting heart rate (HR) and overnight heart rate variability (HRV), while you sleep wearing your Visible Band 2.0.
It uses a four-hour period that starts 30 minutes after you fall asleep. It looks at readings when you are still and ignores times when you are moving. Studies suggest the early hours of sleep are more sensitive to reflect recovery than the whole sleep period.
Why overnight instead of morning?
Overnight measurements are often more consistent because:
They're measured over a longer time period (4 hours vs. 1 minute).
Your body position is more stable during sleep.
Sleep provides a controlled environment: consistent posture, mental state and signal quality.
Morning measurements require more consistency (same position, same time after waking) which is not always easy.
Your overnight HRV may look different from your morning HRV. This is normal. The Stability algorithm accounts for these differences when working out how stable your HRV is compared to your recent baseline.