HR Trend Slope: Is Your Pulse Rising or Falling?
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 shows
The HR trend slope tells you whether your heart rate was drifting up or down across the current measurement window. It is useful for watching a change happen in real time, such as your pulse settling as you breathe slowly or climbing after you stand up.
How this tool calculates it
The tool fits a straight line (linear regression) through your RR intervals in order, beat by beat. It then flips the sign and divides by 100, so that a positive value means heart rate is rising (intervals getting shorter) and a negative value means heart rate is falling (intervals getting longer). 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
Positive
Your pulse was trending upward during the window: for example after moving, talking, standing, or during tension.
Negative
Your pulse was trending downward: common when you sit down, relax, or breathe slowly with longer exhales.
Close to zero
Heart rate was roughly flat. At steady rest this is what you would expect.
Why it can be noisy
Within 15 seconds your heart rate naturally rises and falls with each breath, so the fitted line can tilt one way or the other just because of where the window starts. Camera-based beat timing also has small errors. Look for a consistent sign over half a minute or more rather than reacting to a single value.
A simple experiment
Sit still, let the reading settle, then breathe slowly: about 4 seconds in and 6 seconds out for a minute. Many people see the slope move toward negative values as their pulse eases down. Then stand up and watch it turn positive as heart rate briefly rises.
Important limits
This is a real-time trend indicator for this browser tool. It has no standard normal range and is not a medical measurement.
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
Positive means your pulse is climbing; negative means it is easing down.
Ready to measure?
The ONDA app works with your iPhone camera, Apple Watch and Apple Health.