How ONDA works.
ONDA turns your heartbeat into a live signal you can train against. Here is the loop — from raw pulse to HRV to the coherence score you see on screen — 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
Beat intervals
From that signal ONDA extracts the time between consecutive heartbeats — the beat-to-beat (RR) intervals. This series is the raw material for every heart-rhythm number.
- 3
HRV + rhythm
ONDA computes HRV from the variation in those intervals, and tracks the shape of the heart-rhythm wave in real time as you breathe.
- 4
Live feedback
The current rhythm and a coherence score are shown live, so you can see your body respond to each breath — the biofeedback loop that makes ONDA an active trainer, not a passive tracker.
- 5
Paced breathing
A visual pacer guides you toward slow, even breaths near your resonance frequency (roughly 5–6 breaths per minute), the pace that most strongly organizes the heart rhythm.
- 6
Trend over time
Session by session, ONDA records your resting-HRV baseline and its direction — the long-term signal the practice is designed to move.
How ONDA computes HRV
Heart-rate variability is the variation in the time between heartbeats. ONDA computes it from the beat-to-beat (RR) interval series — primarily as RMSSD (the root mean square of successive differences), the short-term measure most closely tied to parasympathetic (vagal) activity, and reports SDNN where a broader window applies. On Apple Watch, ONDA can use the HRV that Apple Health already derives; from the iPhone camera, it computes HRV from the pulse waveform at rest.
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. Higher, steadier breathing near your resonance frequency tends to raise it.
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.