Ellipsograph of Van Schooten.

A cursor, pivoted on the end (B) of the rod, moves on a straight slot s , the rod CA (manovella) is pivoted on the plane in C and is pivoted on the first rod on the point A where BA=AC=l .When the second rod rotates around C, the point Q of the first rod such as QA= l , describes the line perendicular to s on C, while every other point of the first rod describes an ellipse.