The window "Curve: X(t)" in this demonstration displays the curve X(t) = (cos(t), sin(t), cos(2t)/c), the point X(t0), and the tangent, normal, and binormal vectors T(t0), P(t0), and B(t0), with their tails at that point.

The window "Spherical Images: T, P, B" displays the same three vectors with their tails at the origin, the sphere on which their heads are constrained to lie, and the principal indicatrix. From Jacobi's Theorem, if the principal indicatrix is a simple curve, it will divide the sphere into two equal area regions.

It is possible to change c, t0, and X(t) in the control window. It is also possible to set X(t) equal to circle(t) (listed in the control window).