The graph indicates the time evolution of the angle for the simple pendulum. You can regulate the major parameters.
This allows you to simulate extra-terrestrial values of "g" (g=1.6 on the Moon and g=27 on Jupiter).
You can illustrate the transient responses of this system (SHM, damped ...)
Drag the mass to adjust new initial conditions.
Click and drag the mass to set a new initial angle.