The window "Curve: X(t)" in this demonstration displays the curve X(t)
= (cos(t), sin(t), cos(2t)/c), the point X(t_{0}), and the
tangent,
normal, and binormal vectors T(t_{0}), P(t_{0}), and B(t_{0}),
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, t_{0}, and X(t) in the control window. It is also
possible to set X(t) equal to circle(t) (listed in
the control window).