The wall does not move; the number does

Your beam_watch.py, simulated: one LiDAR beam at a wall 2.00 m away, noise 4 mm.

Starting Python in the browser. The first time takes a few seconds.

Beam noise 4 mm

Your script uses 4 mm. Changing it restarts the run.

Python not started yet.

The Python behind the demo

The page imports beam_watch.py as it is, adds readings with its Stats, and bins them with its histogram().

Your terminal screen, printed by show() for the current run:

$ python3 beam_watch.py --sim