The window "Curve on Domain" displays a domain, a
point P in the domain, the curve P + t(cos(θ), sin(θ)) (where t
runs from 0 to t0), and the point P + (cos(θ),
sin(θ)), which is
the endpoint of the curve that is not P.
The window "Curve on Surface" displays the surface X(u,v) and the image of the curve and two points
in the domain on that surface.
The window "Arclength" displays the
graph of arclength as a function of t0.
It is possible to
drag P in the "Curve in Domain" window and to change t0,
X(u, v) in the control window.