Below is a close approximation of a regular nonagon.

Although a regular nonagon is not constructible with compass and straightedge there are methods of construction that produce very close approximations.

However, the program also allows users to employ transformations to "cheat," creating figures impossible to construct under the traditional compass-and-straight-edge rules (such as the regular nonagon).

With algebraic methods, more specifically applying the machinery of field theory to the number field containing roots of unity, it can be shown that it is not possible to construct a regular nonagon using only compass and straightedge - a purely geometric problem.