The window "Domain" displays a domain, a point (u0, v0) in the domain, a subset of the domain colored white, red, blue, and magenta, and a point on the boundary of this subset.

The window "Surface: X(u, v)" shows the elliptic paraboloid X(u, v) = (u, v, u2 + v2), the images of (u0, v0), and the colored subset of the domain on this surface (with each point in the domain mapped to a point of the same color).

The window "Normal Image" shows the surface produced by mapping each point on the surface X(u,v) to its unit normal vector, preserving the coloring from the "Surface" window.

It is possible to change the point (u0, v0) and the colored subset of the domain by clicking and dragging the points shown in the "Domain" window.