The 3D graph shows the motion of a free-swinging pendulum.

The graph on the upper right is the x-coordinate
(red axis on 3D graph) vs. time, and

the lower right graph is
the
y-coordinate (green axis on 3D graph) vs. time. The two

time
graphs together show how the greatest excursion of
the pendulum
moved between

the x- and y-coordinates. The pendulum swung in
an ellipse that rotated in time.