This demo includes a single graphical window that displays a curve
X(t) (which you may change in the appropriate textbox in the control
window), the parallel curve to X(t), and line segments of length r
normal to X(t) demonstrating the relationship between X(t) and its
parallel curves. To change r, use the following buttons in the control
window:

[<]: Decrease r by one step.

[>]: Increase r by one step.

[<<]: Decrease r until it reaches its minimum
value.

[>>]: Increase r until it reaches its maximum
value.