In mechanical drawing, the steps of making ellipse by concentric circle method are as follows:

1, the long axis AB and the short axis CD of the ellipse are known, and a rectangular coordinate system is established, with the intersection o of the two axes as the origin;

2. Draw two concentric circles, with O as the center and major axis AB and minor axis CD as the diameters;

3. Make several bisectors to intersect with two concentric circles through the center o;

4. The intersection of the bisector and the great circle is a vertical line, the intersection of the bisector and the small circle is a horizontal line, and the point where the vertical line intersects the horizontal line is a point on the ellipse;

5, analogizing all bisectors in turn to determine the points on all ellipses;

6. Connect these points with a curved plate, which is the desired ellipse.

Higher Education Press-Mechanical Drawing (3rd Edition), Chapter 1, Section 3.