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.