Have the calibrator stand on that mark so their entire body is visible in the webcam.
When ready, the calibrator should make the gesture illustrated below.
Once the system has analysed them, enter their actual height.
The Calibration Gesture
Stand facing forward, arms at sides. Sweep one hand in a full circle —
across your body, above your head, and back to your side.
Gesture detected! Enter the calibrator's height:
Calibration saved. The experience is ready for visitors.