The window "Domain" displays a point C and the
curve C + t(cos(a), sin(a)), where t runs from –1 to 1.

The window "Surface" window displays the surface X(u, v), the image of the curve
from the "Domain" window on this surface, the point X(C + t_{0}(cos(a),
sin(a)), and the frenet frame, osculating, normal, and rectifying
planes, and normal vector to the surface, at that point.

The vectors P,
B, and N are also shown in the "P-B plane" window. The normal curvature
of the curve X(C + t(cos(a), sin(a))) at t_{0} is given
by the
curvature of X(C + t(cos(a), sin(a))) at t_{0} times the
dot product
of P and N at t_{0}.

It is possible to change C in the "Domain"
window by
clicking and dragging it, and it is possible to change a, t_{0},
and X(u,
v) in the control window.