Reading the overnight chart
How to read the dual-axis SpO₂ and heart-rate trace for a night.
Updated 2026-06-28
Every session opens on its overnight chart — a single view of how your blood oxygen and heart rate moved across the night.
The two lines
- SpO₂ (green, left axis) runs 70–100%. Healthy sleep sits near the top; sharp dips are desaturation events.
- Heart rate (red, right axis) runs 30–200 bpm. Look for the cyclic rises that often pair with desaturations.
Zoom and pan
- Use the −/+ controls to zoom the time axis, and the ◀/▶ arrows to pan.
- Drag across a region to select it for closer analysis.
- Hit reset to return to the full night.
Zoom into a cluster of dips to see whether they line up with heart-rate swings — that pairing is the signature of cyclic variation of heart rate (CVHR).
Next, see what the numbers behind the chart mean in overnight analysis metrics.