Energy %: An Experimental Heart-Rate Index
Estimated from a single camera (PPG) reading — an educational estimate, not a medical measurement. State labels (Flow, Focus, Alarm…) are rough, experimental patterns, not emotion detection.
What this number is
Energy here is an experimental index, not a measure of how energetic you feel, your fitness, or a "battery". It starts at 90% and goes down when your heart rate is above 75 bpm and when your beat-to-beat rhythm is irregular relative to its average (CSI).
How this tool calculates it
Energy = 90 − 1.5 × (heart rate − 75, if above 75) − 80 × CSI, limited to 10–100%. For example, at 70 bpm with a typical camera CSI of 0.3, Energy is about 66%; at 95 bpm with the same CSI, it is about 36%. The tool works on a rolling 15-second window of fingertip video (about 30 frames per second), finds each pulse peak, keeps only beat-to-beat (RR) intervals between 400 and 1,500 ms that are within 22% of the median, and smooths the displayed numbers so they change gradually.
How to read it
Higher
Your pulse was at or below about 75 bpm and the rhythm looked steady.
Lower
A faster pulse (coffee, movement, heat, stress, illness) and/or an irregular-looking rhythm, which is often just a noisy signal.
Important limits
This is an experimental heuristic built from a few camera-derived inputs. It is not a validated physiological measure, it is not emotion detection, and it is not a medical test. Treat it as a rough hint about the direction your signal is moving, not as a verdict about how you feel. Because of the formula, Energy cannot exceed 90% and a resting pulse below 75 bpm is not rewarded any further.
What actually helps
Sleep
Consistent, sufficient sleep is the strongest lever for daytime energy.
Movement and daylight
A short walk, especially outdoors in the morning, often helps more than extra caffeine.
Short resets
A few minutes of slow breathing can lower a racing pulse and help you feel more settled.
The ONDA app is a separate product: it focuses on pulse, breathing and, with an Apple Watch, coherence. It does not use the formulas on this page.
The ONDA Principle
Energy here drops with a pulse above 75 bpm and an irregular-looking rhythm. It is a rough hint, not a fuel gauge.
Ready to measure?
The ONDA app works with your iPhone camera, Apple Watch and Apple Health.