How ONDA works.
ONDA turns your heartbeat into a live signal you can train against. Here is the loop — from your pulse to HRV, the coherence score you see on screen and your personal baseline — and, just as importantly, what each number is and is not.
The biofeedback loop
- 1
Signal in
ONDA reads your heartbeat — from the Apple Watch optical sensor (or Apple Health), or from the iPhone camera measuring the colour change in your fingertip (photoplethysmography, PPG).
- 2
Pulse, not single beats
The iPhone camera estimates your pulse rate (heart rate) — it does not detect individual heartbeats and cannot measure HRV. With an Apple Watch, ONDA receives heart-rate readings from the watch.
- 3
HRV from Apple Health
ONDA does not compute HRV itself. It reads HRV ready-made from Apple Health as SDNN — the value an Apple Watch (or another device that writes to Apple Health) records there.
- 4
Live feedback
The current rhythm is shown live — plus a coherence score with an Apple Watch — so you can see your body respond to each breath, the biofeedback loop that makes ONDA an active trainer, not a passive tracker.
- 5
Your personal baseline
From values in Apple Health — HRV, resting heart rate and breathing rate — ONDA builds your personal baseline over the last 14 days. It compares your latest day of data with your own corridor — the average of your earlier days with enough data plus or minus one standard deviation — and flags it only when it is at least 1.5 standard deviations outside and has changed by a minimum amount. How the values are taken: the 14-day card averages all of a day’s samples, day by day. For signals, HRV counts only samples recorded before 09:00, at least three a day; resting heart rate is Apple’s daily value; breathing rate uses Apple’s samples, which are usually recorded during sleep.
Where ONDA’s HRV comes from
Heart-rate variability is the variation in the time between heartbeats. ONDA does not calculate it from your heartbeats: it reads HRV ready-made from Apple Health as SDNN, the value an Apple Watch (or another device that writes to Apple Health) records there. The live in-practice variability tile is a simpler heart-rate-variation estimate, not a clinical HRV value. The iPhone camera gives your pulse (heart rate) only; HRV appears once an Apple Watch is connected.
A clean reading needs a stable signal and a short quiet window. Motion, a poor camera contact or an irregular rhythm add noise, so readings are most reliable at rest; when the signal is too poor to trust, ONDA asks you to retake it rather than showing a number it cannot stand behind.
How ONDA computes coherence
When you breathe slowly and evenly, your heart rate rises and falls in a smooth wave that tracks your breath (respiratory sinus arrhythmia). ONDA’s coherence score reflects how smooth, regular and large that oscillation is over a rolling window — in other words, how well your heart rhythm is organized by your breathing right now. Slow, even breathing tends to raise it. The coherence score needs an Apple Watch.
What it is not: coherence is a real-time practice metric, not a clinical biomarker, not a measure of “how healthy” you are, and not comparable across different people as a score of merit. It is a mirror for your practice in the moment.
The boundaries
- • HRV is not a direct measure of “stress”; a higher HRV is not automatically better in every context.
- • The coherence score is not a clinical or diagnostic biomarker.
- • ONDA is not a medical device and does not diagnose, treat or monitor any condition.
For exactly which numbers are measured, derived or estimated, see what ONDA measures; for the evidence behind the method, see the science behind ONDA.