Sit about an arm's length from the camera, facing a window or lamp, and keep still.
Find your pulse on your wrist or neck. Tap the button (or press the space bar) on every beat you feel.
The colour signal after cleaning: each peak is one heartbeat arriving in your face.
Tiny brightness changes in each colour, in percent. Haemoglobin absorbs green light strongly, so green usually carries the clearest pulse.
How strongly each rhythm appears in the signal. The tallest peak is your heart rate.
A face-tracking model finds 468 points on your face. The lab measures your forehead and both cheeks, where skin is thin and full of tiny blood vessels.
About 30 times a second it averages thousands of pixels into one red, green and blue value. The pulse changes them by well under 1%.
A filter keeps only rhythms between 42 and 210 beats a minute. A Fourier transform then finds which rhythm is strongest.
This is a science demonstration, not a medical device. Readings can be wrong, especially with movement, poor light or some skin and camera combinations. Don't use it for health decisions.