Name: Nodal
Author: rownumber

The purpose of the app is to compare HRV-derived metrics across different states like body position (lying, standing, etc.), breathing patterns, or any change you want to test.

Built for my personal use. Not for profit, no ads, no data collection. **Not a medical app**.

Metrics:
- RMSSD - time-domain HRV metric (root mean square of successive RR differences). Higher values generally indicate more parasympathetic activity.
- pNN50 - percentage of successive RR intervals that differ by more than 50 ms. Related to vagal tone.
- Stress Index - Baevsky's Stress Index, derived from RR histogram width (mode amplitude / range).
- SAMP: Total number of RR intervals processed.
- DROP: Count of intervals rejected by the artifact filter.
- SDNN: Standard deviation of all valid RR intervals.
- SD1/SD2: the ratio of vagal to total variability derived from Poincare geometry (displayed as integer × 100). 

Visualization:
- Poincare plot - Real-time SD1 (short-term/parasympathetic) and SD2 (long-term/combined) variability.
- Histogram - Real-time RR interval distribution.

You can set a 20% standard outlier filter or a 30% for deep relaxation to exclude sensor artifacts or ectopic beats. The app uses the generic heart rate sensor API, so a chest strap should work, but I haven't tested one.
Tested exclusively on Venu 3 hardware. The app may retry the sensor connection (typically connects within three attempts on Venu 3). If it never connects on your device, there's probably not much I can do to fix it.

I plan to add more metrics and visualization options over time.